JPH0626920Y2 - Toner density control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a toner concentration control device that constantly detects the toner concentration in a developing device used in an image forming apparatus.

[Prior art]

A developing device is used as one of image forming process means in an image forming apparatus such as a liquid crystal printer, a laser beam printer and a copying machine. This developing device stores a mixed developer of toner and carrier in a developing container and develops an electrostatic latent image on a latent image carrier such as a photosensitive drum with the toner. Since the developing device as described above performs good development, it is necessary to accurately detect the toner concentration in the developer and keep it constant. For this reason, conventionally, the developing device is provided with a toner concentration sensor for detecting the toner concentration. Further, in recent years, since many developing devices are unitized and disposable, the toner concentration sensor described above is provided separately from the developing device, and when the developing device is set in the image forming apparatus, the toner concentration sensor also contacts the developing device. The one that detects the toner density in the developing device is used.

[Problems of conventional technology]

However, since the toner concentration sensor as described above is provided separately from the developing device, the toner concentration sensor may not come into complete contact with the developing device, resulting in variation in the distance between the toner concentration sensor and the developer. That is, when the developing device is set in the image forming apparatus, the toner concentration sensor moves so as to come into contact with the developing device, but the setting position differs depending on the developing device. The reason for this is that there are variations in the thickness of the container of the developing device and in the mechanical parts that bring the toner concentration sensor into contact with the developing device, and it is difficult to maintain a constant distance between the developer in the developing device and the toner concentration sensor. is there. In addition, even if the precision of the parts is improved, the variation in the distance of about 0.1 to 0.2 mm cannot be avoided in actual measurement.

FIG. 7 (a) illustrates the difference in toner concentration detected by the toner concentration sensor when the distance between the toner concentration sensor and the developer varies as described above, and FIG. 7 (b) shows FIG. 6 is a diagram showing a relationship between a distance a ′ and a stable toner density when toner density control is performed with the reference voltage of the comparator kept constant. As shown in (a) and (b) of the figure, if the distance (a ') between the toner concentration sensor and the developer is 0.1 mm, the output voltage of the toner concentration sensor will be greatly different, resulting in stable toner. Concentration is also very different. For example, the distance a'is 0.6m
When m is m, the toner density is controlled to 9%, and the distance a'is shifted for the above-mentioned reason. When the distance a'is 0.7 mm, the toner density is controlled to 7%. Therefore, in this case, 2
%, A toner density control error will occur.

Therefore, the conventional toner concentration control device using the toner concentration sensor cannot control the toner concentration of the developer constantly due to the variation in the distance a '.

[Purpose of device]

In view of the above-mentioned conventional drawbacks, the present invention aims to provide a toner concentration control device having a toner concentration sensor provided separately from a developing device, which is capable of always detecting a constant toner concentration. And

[Key points of device]

The present invention is a toner for controlling the toner concentration with respect to a carrier in a developer for developing an electrostatic latent image on an electrostatic image bearing member by using a concentration detection sensor provided separately from a container accommodating the developer. In the concentration control device, reference potential generating means for sequentially generating a plurality of reference potentials in response to a predetermined signal output from the container and indicating that the container is unused, and output from the reference potential and the concentration detection sensor. A comparing means for comparing the output state of the comparing means, a storing means for storing the coded reference potential according to the output of the detecting means, and a code signal stored in the storing means. Output prohibiting means for prohibiting the output of the predetermined signal after being output.

[Example of device]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic configuration diagram of a liquid crystal printer using the toner density control device of the present invention.

In the figure, a photosensitive drum 1 is rotatably supported at a substantially central portion of a liquid crystal printer, and is rotationally driven at a predetermined speed in a direction of an arrow. A charger 2, a liquid crystal shutter, etc. for uniformly charging the surface of the photoconductor drum 1 are provided around the photoconductor drum 1 along the rotation direction thereof, and light corresponding to image information input is provided. A liquid crystal head 3 for irradiating the surface of the photosensitive drum 1 with a signal to form an electrostatic latent image; a developing device 4 for supplying toner to the formed electrostatic latent image to form a toner image;
A transfer device 5 for transferring the toner image onto the paper P and a cleaner 6 for removing the toner remaining on the photosensitive drum 1 without being transferred onto the paper P by the transfer device 5 are provided. Below the photoconductor drum 1, a paper feed cassette 7 in which the paper P is stacked and stored, a paper feed roller 8 that carries out the paper P one by one from the paper feed cassette 7, and a transport roll pair 9 that carries the paper P. A fixing device 10 and the like for fixing the toner image on the paper P after transfer are provided.

Further, the photosensitive drum 1, the charger 2, and the cleaner 6 described above are configured as an integral drum unit DU so as to be attachable to and detachable from the main body of the liquid crystal printer. Further, a toner hopper 4a containing the toner to be replenished to the developing device 4 is provided on the developing device 4 described above. This toner hopper 4a
The developing device 4 integrally forms a toner unit TU, and is also detachably attached to the liquid crystal printer body.

FIG. 1 is a sectional view for explaining in detail the configuration of the toner unit TU configured as described above. As described above, the toner unit TU is composed of the developing device 4 and the toner hopper 4a, and when the toner unit TU is mounted on the liquid crystal printer, the toner density sensor 13 provided on the liquid crystal printer side comes into contact with the side surface of the developing device 4. Is. That is, the holding plate 16 is rotatably attached to the rotary shaft 15 attached to the housing 14 formed in the main body of the liquid crystal printer. Further, the toner density sensor 13 is provided at one end of the holding plate 16, and when the toner unit TU is attached to the liquid crystal printer, the toner unit TU pushes down the upper surface 17 at the other end of the holding plate 16, and the dotted line in the figure. The holding plate 16 located at the position moves to the position indicated by the solid line, and the toner concentration sensor 13 contacts the side surface of the developing device 4.

The developing device 4 stores a developer in which a toner and a carrier are mixed in a developing container 4b, and a developing sleeve 18 is disposed below the developing container 4b in the vicinity of the peripheral surface of the photosensitive drum 1. There is. A magnet roll 19 is arranged in the developing sleeve 18. Further, above the developing sleeve 18, there is provided a doctor blade 22 which holds the developing sleeve 18 at a predetermined distance and cuts the developer into a predetermined thickness.

Further, in the developing container 4b, a stirring roll 20 is provided in order to sufficiently stir the toner and the carrier contained in the developing container 4b.
Is provided.

On the other hand, toner for replenishment is stored in the toner hopper 4a, and the replenishment roll 21 is rotated by driving a solenoid in a control circuit described later, so that the opening 4 of the toner hopper 4a is rotated.
Toner is replenished into the developing device 4 from a '.

Further, the side surface of the developing container 4b with which the above-mentioned toner concentration sensor 13 comes into contact is formed in a concave shape, and its thickness is a as shown in FIG.

The toner concentration sensor 13 is a sensor that detects the toner concentration of the developer by detecting a change in magnetic permeability based on the mixing ratio of the toner and carrier contained in the developing container 4b via the side surface of the developing container 4b. . As shown in FIG. 3, the toner concentration sensor 13 has a characteristic that its output voltage decreases as the toner concentration increases. The toner density data (voltage value) detected by the toner density sensor 13 having such characteristics is output to the control board 23 having the control circuit shown in FIG. The relationship between the power supply and the signal input / output between the toner density sensor 13 and the control board 23 is as follows.
As shown in the figure, +5 V is output from the output terminal O of the control board 23 to the toner density sensor 13 as a power supply voltage, and the toner density data (voltage value) is output from the toner density sensor 13 to the input terminal I ₁ of the control board 23. Is output. Further, the toner concentration sensor 13 is grounded via the input terminal I ₂ of the control board 23.

The control board 23 includes a CPU 24 and an EEPROM (Electrica).
lly Erasable Programmable ROM) 25, comparator 2
6, a data selector 27, a counter 28, and a control circuit including a large number of transistors, resistors, and the like are provided.

The output voltage value of the toner concentration sensor 13 input to the above-mentioned input terminal I ₁ is directly input to the (−) input terminal of the comparator 26. On the other hand, to the (+) input terminal of the comparator 26, a voltage obtained by dividing +5 V by the combined resistance of the resistor R ₁ and R _{2 to} R ₆ is input. The resistors R _{2 to} R ₆ are
As shown in the figure, except that one end of the resistor R ₂ is directly grounded, the resistors R _{3 to} R ₆ are grounded via the transistors Q _{4 to} Q ₁ , respectively. Then, whether or not one ends of the resistors R _{3 to} R ₆ are grounded is determined by the corresponding transistors Q ₄ to Q.
It is determined by supplying a high (H) or low (L) signal to the base terminal (B) of ₁ as described later.
For example, if the L signal is supplied to all the base terminals of the transistors Q _{4 to} Q ₁ , only the resistor R ₂ will be grounded, and the voltage V _{N at} the (+) input terminal of the comparator 26 will be the resistors R ₁ and R _2. By It becomes the voltage of. Further, for example, if the H signal is supplied only to the base terminal of the transistor Q ₄ , the resistors R ₂ and R ₃ are grounded, and the voltage V _N is the resistors R ₁ , R ₂ , and R _3.
Due to the combined resistance of Is applied to the (+) input terminal of the comparator 26.

Further, a resistor R ₇ is also connected to the comparator 26 so that it has a hysteresis characteristic and operates stably even with respect to a gentle input change. In addition, the output of the comparator 26 is the pull-up resistor R _{8 from the} 5V power source.
Are connected via the reference voltage V _N , and the voltage V _I applied to the (−) input terminal is lower than the reference voltage V _{N, the} H level, and conversely, the H level, the L level. The output of the comparator 26 is output as a TL signal to the input terminal I _{5 of the} CPU 24. Further, the AND gate 30 is provided via the inverter 29.
Is also output to.

On the other hand, the CPU 24, in addition to the above-mentioned input terminal I ₅ , also has input terminals I _{0 to} I ₃ , I ₄ and output terminals O ₀ , O _{1 to} O ₄ ,
It has O ₅ , O ₆ , and O ₇ , and the input terminal I ₄ is a new product T for shifting the CPU 24 described later to the automatic adjustment mode.
The U detection circuit 31 is connected.

The new TU detection circuit 31 inverter 31 as shown by a dotted line in the drawing ', a fuse 32, a resistor R _9. The fuse 32 is provided in the above-mentioned toner unit TU, and when the toner unit TU is attached to the liquid crystal printer main body, the terminals J ₁ , J _{2 of the} control circuit (control board 23) are provided.
The fuse 32 is connected to the. The output terminal O ₆ of the CPU 24 is connected to the inverter 33 and the resistor R.
_The transistor Q ₅ is connected via ₁₀ and when the H signal is output from the output terminal O ₆ , the transistor Q ₅ is turned on and a current is supplied to the fuse 32 via the fusing resistor R _11. . Since the resistance value of the fusing resistor R ₁₁ is small and the current flowing through the resistor R ₁₁ is large, the fuse 32 is blown when the transistor Q ₅ is turned on.

In addition, the CPU 24 uses the input / output terminal I / O to perform EEPR.
It is connected to the OM25. When the main power supply of the apparatus is turned on, a reset (RES) signal is output from the above-mentioned output terminal O ₀ to the R terminal of the counter 28 to reset the count value of the counter 28 (set to “0”).

After the counter 28 is reset by the RES signal, the clock (CL
K) A signal is input from the input terminal a and the count is sequentially incremented. The count value to be counted up is output from the output terminals A to D of the counter 28 as 4-bit data to the input terminals 1B to 4B of the data selector 27. In the data selector 27, the 4-bit data of either the input terminals 1A to 4A or 1B to 4B is input to the input terminal S.
Select by a check (CHK) signal input from, and once the selected data is inverted (for example, "0" data is converted to "1", "1" data is converted to "0"), and then output terminals 1Y to 4Y Inverter 36-39 and CPU2
4 to the input terminals I _{0 to} I ₃ . For example, CPU2
When the CHK signal output from the output terminal O _{5 of} No. 4 is the H signal, the 4-bit data from the counter 28 input to the input terminals 1B to 4B is inverted and output to the inverters 36 to 39, and the CHK signal is the L signal. At this time, the data DT2 from the CPU 24 input to the input terminals 1A to 4A is inverted and output to the inverters 36 to 39.

In the inverters 36 to 39, the data input from the data selector 27 is inverted again and supplied to the B terminals of the transistors Q _{1 to} Q ₄ described above via the resistors R _{12 to} R ₁₅ . Transistors Q _{1 to} Q ₄ are the H signal or L input to the B terminal.
Depending on the signal, it is turned on or off, and the resistors R _{6 to} R ₃ described above are used.
Connect or disconnect to ground. At this time, the resistances R _{6 to} R ₃
Assuming that the resistance value of the resistor R ₂ is R, the resistance value of R ₆ ′ is 16 × R, the resistance value R ₅ ′ is 8 × R, and the resistance value R ₄ ′.
Is set to 4 × R and the resistance value R ₃ ′ is set to 2 × R.

Then, how the combined resistance R ′ of the resistors R ₂ and R _{6 to} R ₃ changes in response to the change in the ON or OFF state of the transistors Q _{1 to} Q ₄ will be described below.

However, in the above table, "0", the transistor _Q 1 ~Q ₄
Is turned off, and "1" indicates that the transistor Q ₁ ~
Indicates that Q ₄ is on.

For example, when the combined resistance R'is (16/31) R,
The transistors Q _{1 to} Q ₄ are all on and _one ends of the resistors R _{2 to} R ₆ are all grounded. When the combined resistance R ′ is 16 / 30R, only the transistor Q ₁ is turned off, the other transistors Q _{2 to} Q ₄ are turned on, and the resistance R
₂ and one end of R ₃ , R ₄ and R ₅ is grounded.
After that, the combined resistance R'increases sequentially from 16 / 29R to 1R.

The operation of the toner density control device having the above structure will be described below.

When a main power source (not shown) of the liquid crystal printer main body is turned on, power is supplied to the CPU 24, and if the CPU 24 determines that the toner unit TU is new, the CPU 24 performs an initial setting operation. Whether or not the toner unit TU is new is determined by a signal input from the input terminal I ₄ . That is,
When the toner unit TU is new and is mounted on the liquid crystal printer, the fuse 32 is also connected to the new TU detection circuit 31 through the control boards J ₁ and J ₂ as shown in FIG. 4, as described above. At this time, the output terminal O _{6 of the} CPU 24 is at the L level, which will be described in detail later, and the transistor Q ₅ is in the off state. Therefore, when the new toner unit TU is mounted, the fuse 32 is not blown, so the pull-up resistor R ₉ is grounded through the fuse 32, and the H signal is input to the input terminal I ₄ through the inverter 31 ′. It has been entered. Therefore, the initial setting operation is performed by judging that the H signal is input to the input terminal I ₄ . At the time of this initial setting operation, the CPU 24 outputs the RES signal to the counter 28 and resets all the data in the counter 28 to "0". Thereafter, as shown in the time chart of FIG. 5, the CPU 24 sets the CHK signal to the H signal and outputs the H signal to the data selector 27. This causes the data selector 27 to invert the data from the counter 28 to the input terminals 1B to 4B and output it to the output terminals 1Y to 4Y.

Further, the AND gate 30 sequentially supplies the clock signal to the counter 28 while the TL signal is at L level. Therefore, in synchronization with the count up of the counter 28, the count value is output to the transistors Q _{1 to} Q ₄ via the data selector 27, the inverters 36 to 39, and the resistors R _{12 to} R ₁₅ .

Then, the output voltage of the toner concentration sensor 13 is set to the control board 2
When the combined resistance R ′ is the smallest, a small voltage is applied to the (+) input terminal of the comparator 26 when supplied to the (−) input terminal of the comparator 26 via the input terminal I ₁ of _No. 3 of FIG. Then, the output of the comparator 26 becomes L, and the TL signal is at L level.

In this state, the CLK signal is sequentially input to the counter 28, the count data is incremented, and the voltage value to the (+) input terminal of the comparator 26 is increased. Then, when the count value reaches a certain count value, for example, the count value "8" shown in FIG. 5, the voltage applied to the (+) input terminal of the comparator 26 becomes larger than the voltage V _I , and the output signal of the comparator 26 becomes high. The TL signal to H level. When the TL signal becomes H level, the gate of the AND gate 30 is closed, the CLK signal is not input to the counter 28, and the counter 28 stops in that state. When the TL signal becomes H level, the CPU 24 knows that the automatic adjustment is completed, and the count value being output from the output terminals 1Y to 4Y at that time is inverted by the inverter 40 to obtain the data DT1 as I _{0 to} I _3.
From the CPU 24, and the captured data is E
Write in a predetermined area of the EPROM 25. As described above, the data DT1 written in the EEPROM 25 is
When a new toner unit TU is set in the liquid crystal printer and the input terminal I _{4 of the} CPU 24 is at the H level, the CPU 2
Reference numeral 4 is adjustment data obtained by automatically controlling the reference potential of the comparator 26. Next, when the above adjustment is completed, C
The PU 24 momentarily outputs the H signal from the output terminal O _6, and outputs the low signal to the transistor Q ₅ via the inverter 33 and the resistor R ₁₀ . The transistor Q ₅ is turned on by the input of this low signal, and the fuse 32 is turned on via the fusing resistor R _11.
A current is applied to blow the fuse 32.

After that, at the time of normal operation, that is, the L signal is input to the input terminal I ₄ , the above data is read from the EEPROM 25 when the main power is turned on, and the data DT2 (DT2
= DT1), the CHK signal is output to the data selector 27 and can be used as the reference voltage of the toner sensor by changing the CHK signal to the L signal.

That is, as described above, the density data detected by the toner density sensor 13 when the new toner unit TU is attached indicates that the toner density of the developer is optimum, and from the characteristics of the toner density sensor 13 shown in FIG. If the toner density is lower than this, the voltage value output to the (-) input terminal of the comparator 26 becomes high, and the TL signal becomes L level. Therefore, when the TL signal becomes L level during the image forming operation, a signal is output from the output terminal O ₇ to the solenoid 41 via the inverter 42 to turn on the solenoid 41, thereby rotating the replenishment roll 21 to rotate the toner. Is supplied to the developing device 4. By this replenishment, the toner density in the developing device 4 can be always kept constant.

Moreover, when the toner unit TU is mounted on the liquid crystal printer, even if the distance a'between the toner concentration sensor 13 and the developer is varied as shown in FIG. 6, the EEPROM 25 is adapted to the distance a'as described above. Since the reference potential is stored, the error is automatically corrected. For example, if the distance when a new toner unit is attached is a ₀ ′, the toner concentration sensor output is V _{0 and the} reference potential is also set to V ₀ , and if the distance is a ₁ ′, the toner concentration sensor output is V ₁ . The reference potential is also set to V ₁ , and if the distance is a ₂ ′, the toner concentration sensor output becomes V _{2 and the} reference potential is also set to V ₂ . That is, the difference between the standard voltage V ₀ and ΔV ₁ , ΔV
₂ will be absorbed.

In this embodiment, the combined resistance R ′ is set by five resistances R _{2 to} R ₆ , but if the number of resistances is increased, finer adjustment can be performed. Further, the same operation can be performed by using a combination circuit of ladder resistors such as R-2R.

[Effect of device]

As described in detail above, according to the present invention, even if there is a variation in the distance between the toner concentration sensor and the developer, the variation is automatically corrected by the control circuit so that a constant toner concentration can be detected. It can be carried out.

[Brief description of drawings]

FIG. 1 is a sectional view of a developing device in which the toner concentration control device of this embodiment is used, FIG. 2 is a schematic configuration diagram of a liquid crystal printer in which the toner concentration control device of this embodiment is used, and FIG. FIG. 4 is a characteristic diagram of the density sensor, FIG. 4 is a circuit diagram of a developing device in which the toner density control device of this embodiment is used, and FIG. 5 is an operation of the developing device in which the toner density control device of this embodiment is used. 6 is a characteristic chart for explaining automatic correction of a developing device in which the toner control device of this embodiment is used, and FIGS. 7 (a) and 7 (b) are a toner concentration sensor and a developer. It is a characteristic diagram with respect to the distance of. 4 ... Developing device, 4a ... Toner hopper, 13 ... Toner concentration sensor, 24 ... CPU, 25 ... EEPROM, 26 ... Comparator, 27 ... Data selector, 28 ... Counter, 32 ... Fuse, 41 ……solenoid.

Claims (1)

[Scope of utility model registration request] 1. A toner concentration of a carrier in a developer for developing an electrostatic latent image on an electrostatic image bearing member is controlled by using a concentration detection sensor provided separately from a container accommodating the developer. In the toner concentration control device, a reference potential generating unit that sequentially generates a plurality of reference potentials in response to a predetermined signal output from the container and indicating that the container is unused, from the reference potential and the density detection sensor. Comparing means for comparing the output of the comparing means, detecting means for detecting the output state of the comparing means, storing means for encoding and storing the reference potential according to the output of the detecting means, and a code signal for the storing means. A toner concentration control device for inhibiting the output of the predetermined signal after being stored.