JPH0425491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for detecting toner concentration in a magnetic brush developing device using a dry two-component developer in an electrophotographic copying device or the like.

For example, in an electrophotographic copying machine, a magnetic brush developing device that uses a dry two-component developer made of a carrier made of a magnetic material such as iron powder or ferrite mixed with toner particles always maintains the image density of the copy constant. To do this, the mixing ratio of toner in the developer must always be maintained within a predetermined range. For this purpose, it is necessary to constantly detect the toner concentration of the developer and replenish toner according to the amount of toner consumed. On the other hand, if this toner density detection is not performed accurately, the image density of the copied image will fluctuate significantly or background fog will occur, resulting in problems in which the copying apparatus cannot perform its original functions.

As a conventionally known toner concentration detection method,
A method of detecting the magnetic permeability of a developer, a method of detecting the bulk specific gravity, and a method of measuring the optical reflectance are known. However, the method of measuring magnetic permeability has the disadvantage that it is necessary to detect slight changes in magnetic permeability in the developer, and the detection signal varies greatly depending on the toner charge rate and the degree of agitation of the developer. In the detection method, since the specific gravity of the toner is much smaller than the specific gravity of the carrier, changes in the amount of toner in the developer can only be detected with a small output, and the output value fluctuates depending on the fluidity of the developer and the degree of agitation. It has the disadvantage that highly accurate detection is difficult. In view of the above-mentioned circumstances, the present invention relates to a method of detecting toner concentration by detecting optical reflectance.
Conventional optical toner concentration detection devices have the following drawbacks.

This method of measuring optical reflectance detects the amount of toner in the developer using the difference in reflectance between toner particles and carrier particles. Kosho 38-17245
As shown in the above publication, a method is known in which a measuring section is provided on the wall of a developer storage section. However, this method has the disadvantage that toner accumulates on the detection window and the detection ability deteriorates over time.Also, the fluidity of the developer near the detection window is poor, and the toner in the developer that actually contributes to development The disadvantage is that the concentration cannot be detected accurately. On the other hand, a method has been proposed in which the optical reflectance of the developer held on the developing roller is directly detected, as shown in Japanese Utility Model Application Publication No. 49-8403. This solves the fluidity problem, but it does not eliminate the drawback that the detection window on the front of the sensor gets dirty with toner.Furthermore, the level of the detection signal is generally lower because the detection is performed while the developer is in contact with the detection window. Therefore, the S/N of the detection signal is also poor, resulting in a problem that the detection accuracy is reduced. Another method is JP-A-52-130644.
As shown in US Pat. No. 4,112,870, a method has been proposed in which pressurized air is blown onto the sensor section to prevent the detection window from becoming dirty; however, this method does not prevent the detection window from becoming dirty. However, it has the disadvantage that fine toner particles are scattered to the outside of the developing device by the air flow, and the entire device is contaminated with toner.

An object of the present invention is to prevent the detection window from being contaminated by toner and maintain a constant state of cleanliness at all times, thereby making it possible to perform stable detection over time and to prevent toner from forming on the detection window during detection. It is an object of the present invention to provide an optical toner concentration detection device that can obtain a detection signal with a high level and low noise because there is no contact, and can perform highly accurate detection over a long period of time.

The present invention provides a device for detecting toner concentration in a developer in a magnetic brush developing device that performs development using a dry two-component developer using a developing roller having a sleeve made of a non-magnetic material and a magnetic roller disposed inside the sleeve. a light source that emits light toward the developer; a photodetector that receives light reflected from the developer; a transparent plate arranged at intervals such that it contacts the part but does not come into contact with the part where the ears are not standing; and a means for rotating the edge-cutting magnet roller;
While the magnet roller is rotating, the reflectance of the developer is determined based on the signal output from the photodetector when the non-spiked portion of the developer passes through the front surface of the transparent plate, and the toner concentration is determined. The invention is characterized by comprising a means for detecting.

In the present invention, the detection window is arranged to face the developing roller, and when the magnetic pole part of the magnet roller passes, the raised part of the developer is brought into contact with the detection window to clean the detection window, and the magnetic poles are separated from each other. When the intermediate part of the developer that does not stand up passes, the developer layer is arranged so as to be separated from the detection window, and the reflectance of the developer is detected when this intermediate part passes. It is designed to obtain level signals.

The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a configuration diagram showing an example of a developing device equipped with a toner concentration detection device according to the present invention. The toner particles made of a non-magnetic insulating material and the carrier made of a magnetic material are triboelectrically charged so that the toner particles are positively or negatively charged, and the carrier is charged with a polarity opposite to that of the toner particles. The developer is constructed such that toner particles adhere to the surface of the carrier due to electrostatic attraction acting between the toner and the carrier. This developer is housed in the housing 2 of the developing device 1. A developing roller 3 is arranged within the housing 2. This developing roller 3 is uniformly S in the longitudinal direction.
It consists of a magnet roller 4 whose poles and north poles are alternately magnetized, and a sleeve 5 made of a non-magnetic material. The developer is conveyed on the sleeve 5 in a direction opposite to the direction of rotation of the magnet roller 4 while being held on the sleeve 5 by the magnetic force of the magnet roller 4. In this example, since the magnet roller 4 rotates clockwise, the developer rotates counterclockwise on the sleeve 5. The developer held on the sleeve 5 is regulated into a layer of constant thickness by a height regulating plate 6 called a doctor blade, and then transferred to a drum-shaped charge carrier 2 on which an electrostatic latent image is formed.
The electrostatic latent image formed on the charge holding body 21 is conveyed to the development area 22 facing the charge holding body 21 and developed. After development, the toner toner passes under the toner concentration detection device 12 which is arranged to face the developing roller 3, and is then separated from the sleeve 5 by the scraper 7 and conveyed to the stirring device 8. Toner is stored in the toner replenishment hopper 9, and a certain amount of toner is replenished to the stirring device 8 via the toner replenishment roller 10 based on a toner replenishment command to be described later. Then, it is uniformly mixed and stirred with the developer conveyed from the scraper 7 and used for development.

FIG. 2 is a diagram showing the distribution of developer on the developing roller 8. As shown in FIG. Since the magnetic roller 4 has S and N magnetic poles alternately magnetized in the circumferential direction and uniformly in the longitudinal direction, the magnetic field formed by the magnetic roller 4 is directed outwardly by the normal to the roller in the magnetic pole portion. The intermediate portion between the magnetic poles is formed to face approximately in the circumferential direction. A layer of developer is formed on the sleeve 5 along the magnetic field generated by the magnet roller 4. Therefore, the developer stands up in the portions corresponding to the magnetic poles of the magnet roller 4, forming thick, unevenly arranged spiked portions 20a, and the magnetic field is uniform in the circumferential direction at the intermediate portion between the magnetic poles. Since the layered portion 20b is formed thinly and has a smooth and dense layer surface, a dense layered portion 20b is formed. Therefore, as the magnet roller 4 rotates, the thick, non-uniform spiked portion 20a and the thin, uniform layered portion 20b alternately pass in front of the toner concentration detection device 12.

FIG. 3 is a configuration diagram showing an example of a toner concentration detection device according to the present invention. In the figure, numeral 13 is a light source, which is preferably a light emitting diode that generates little heat and has excellent light quantity stability. Reference numeral 14 denotes a photodetector, which includes a silicon photodiode, a phototransistor, and the like. Reference numeral 15 is made of an opaque material and has an opening 15a for guiding light from a light source and an opening 15b for guiding reflected light from the developer 20, and has a light source 13 and a photodetector 14 mounted on the back side. Element block 16 indicates a transparent plate closely attached to the front surface of element block 15 to form a detection window and prevent developer from entering inside. The light emitted from the light source 13 passes through the aperture 15a, passes through the transparent plate 16, is irradiated onto the developer 20, is absorbed or reflected, and a portion of the light reaches the photodetector 14, where the reflectance of the developer is detected. . Then, this reflectance is converted into a toner mixing ratio, and the toner concentration in the developer is detected. Transparent plate 1 forming a detection window of toner concentration detection device 12
The distance between the developer layer 6 and the developer 20 is such that when the spike portion 20a of the developer layer passes, the developer layer is close to the transparent plate 16.
The developer layer and the transparent plate 16 are set so that they do not come into contact with each other when the layered portion 20b that does not stand up passes. With this arrangement, as the magnet roller 4 rotates, the surface of the transparent plate 16 constituting the detection window alternately comes into contact with and out of contact with the developer 20, and the developer 20 rises in the raised portion 20a.
is cleaned and maintained in a constant state of cleanliness. FIG. 3a shows the state when the magnetic pole of the magnet roller 4 is positioned in front of the transparent plate 16. Since the magnetic field is formed in the outward normal direction, the developer 20 stands in spikes in the outward normal direction of the developing roller and is arranged in a non-uniform and unstable state. In this case, the irradiated light from the light source 13 penetrates deep into the developer 20 and is repeatedly reflected many times, so the light detector 14
The reflected light received by the sensor is weak and unstable. FIG. 3b shows the state when the intermediate portion between the magnetic poles of the magnet roller 4 is located in front of the transparent plate 16. Since the lines of magnetic force of the magnet roller 4 are formed approximately along the circumferential direction of the sleeve 5, the developer is arranged in a dense state with a smooth surface, and the transparent plate 16
It is in a state of separation from. Since the surface of the developer layer is smooth and the developer is densely arranged, the light emitted from the light source 13 does not go around much inside the developer 20 and is mainly reflected from the surface and reaches the photodetector 14. As a result, the photoelectric output from the photodetector 14 is large and a stable detection signal with little noise can be obtained.

FIG. 4 is a diagram showing photoelectric output when toner concentration is measured using the toner detection device according to the present invention. The vertical axis shows the relative value of the output voltage, and the horizontal axis shows time. The developer used was an oxidized iron powder carrier of 150 to 250 mesh and toner with an average particle size of 11 microns. #1 has a toner mixing ratio of 8% (weight ratio),
#2 shows the output for 6% developer, and #3 shows the output for 4% developer. In #1 to #3, the detection signals are low level signals X ₁ , X ₂ , X ₃ and high level signals
Y ₁ , Y ₂ , and Y ₃ are detected alternately. The low level signal is a detection output when the spiked portion 20a of the developer passes, and the signal level is low and at the same time contains many noise components. The high level signal is a detection output when the developer passes through the layered portion 20b between the magnetic poles of the magnet roller 4, where the developer is densely and uniformly distributed, and the level is high and at the same time the noise component is small. There are characteristics. Such a difference can be easily understood from the explanations in FIGS. 3a and 3b. In addition, overall, compared to the detection output when the magnetic pole part of the magnet roller passes, the detection output when the intermediate part between the magnetic poles passes has a larger difference in detection output due to the difference in toner density. , it has also been shown that there is a more accurate detection ability. The optical reflectance of developer has a stable value under various conditions, but the light source, photodetector, signal processing circuit, etc. used to detect this reflectance changes due to changes in temperature. Therefore, it is inevitable that the output characteristics will change. In particular, when the detected photocurrent is small, the dark current of the photodetector or signal processing circuit becomes a value that cannot be ignored, and the dark current increases rapidly due to temperature rise, causing a detection error.
Since these dark currents exist independently of the detection output, it is necessary to maintain the photoelectric detection output at a high level in order to avoid being affected by them.

In the toner concentration detection device according to the present invention, the transmitting plate 16 is cleaned by passing the raised portion of the developer at least once in front of the detection window, so it is limited to the magnetic roller single rotation development method. First, it can be applied to developing apparatuses of all developing methods, including a developing method in which a sleeve and a magnet roller simultaneously rotate, and a developing method in which a sleeve rotates independently. Among these, in a sleeve single rotation developing type developing device, the magnet roller is rotated when an area where no electrostatic latent image is formed on the charge carrier passes through the development area, such as between copies. This makes it possible to achieve the present invention.

Although the detection signal obtained by the toner concentration detection device according to the present invention periodically includes a high level signal and a low level signal as shown in FIG. 4, it cannot be used as a detection signal as it is. Therefore, it is necessary to sample the high level signal of the detection signal, that is, the signal when the intermediate portion between the magnetic poles of the magnet roller passes through the detection window, and shape the sampled signal to use it as the toner concentration detection signal. . FIG. 5 is a block diagram showing an example of a circuit configured to obtain a control signal for toner replenishment at the same time as sampling by comparing a preset reference voltage with a signal voltage from a photodetector. In the figure, the detection signal obtained by the photodetector 14 has a waveform as indicated by α. This signal is amplified by an amplifier circuit 41 and applied to a voltage comparison sampling circuit 42. A reference voltage serving as a reference for the toner mixture ratio is applied from the reference voltage generation circuit 43 to the voltage comparison sampling circuit 42 and compared with the amplified detection signal. When the toner mixing ratio is lower than the reference level, the high level signal obtained when the intermediate portion between the magnetic poles of the magnet roller 4 passes among the amplified detection signals becomes higher than the reference voltage. Therefore, an ON signal obtained by sampling only the high level signal is obtained, and β indicates the signal obtained in this way. Note that high frequency components contained in the detection signal are removed by incorporating a high frequency bypass filter into the amplifier circuit or the like. Since the signal indicated by β is a periodic ON signal, this signal cannot be used as a control signal for controlling toner replenishment. The shaping circuit 44 is a circuit for converting a signal denoted by β into a continuous control signal, and its output is denoted by γ. The operating principle of the shaping circuit 44 can take various methods, but as an example, it includes a delay circuit that delays the signal for a certain period of time, and stretches the ON signal generated every cycle to the length of one cycle T. Various configurations are applicable. The control signal generation circuit 45 is a circuit for converting the signal thus obtained into a voltage or impedance suitable for driving a toner replenishing device such as a motor or solenoid. Then, based on the signal from the control signal generation circuit 45, the toner replenishing device 10 is operated to replenish toner, so that the toner mixing ratio of the developer is always maintained constant. The configuration shown in FIG. 5 samples the detection signal from the photodetector 14 and
Although this is an example of a configuration in which the signal is converted into an ON-OFF signal, a configuration in which the detection signal from the photodetector 14 is sampled to obtain an analog signal corresponding to the toner mixture ratio may also be applied. FIG. 6 is a block diagram showing an example of this. The sampling circuit 46 in the figure is one that acts as a gate circuit,
Its opening/closing is performed by a signal from the sampling signal circuit 47. The sampling signal circuit 47 detects a high level signal based on the signal from the photodetector 14, generates a sampling signal, and generates a signal for turning the gate of the sampling circuit 46 on and off. Photodetector 1 is an example of a sampling signal circuit.
4 is detected as an average voltage through a low-pass filter and used as a reference signal, and this reference signal is compared with the signal from the photodetector 14.
A configuration can be applied in which an ON signal is generated when the signal from the reference signal is larger than the reference signal. The signal obtained from the sampling circuit 46 is a signal obtained by extracting only the high level signal from the signal obtained by the photodetector 14, and is a periodic signal whose peak value corresponds to the toner concentration. It is. Shaping circuit 4
4 is a circuit that converts this signal into a form suitable for the purpose of use; for example, the shaping circuit 4 explained in FIG.
4, it can be converted into a continuous signal by using a configuration including a delay circuit. The signal obtained by the shaping circuit 44 is a continuous signal having a magnitude corresponding to the toner concentration, and is compared with the reference voltage given from the reference voltage generation circuit 43 in the determination circuit 48 to turn it ON.
-OFF signal is generated and passed through the control signal generation circuit 45 to generate a drive signal for toner replenishment.

FIG. 7 is a block diagram showing an embodiment configured to generate a sampling signal using an external signal. The level of the detection signal from the photodetector 14 changes depending on whether or not the raised portion of the developer faces the detection window of the toner concentration detection device.
Since the spikes of the developer correspond to the magnetic pole position of the magnet roller 4, a sampling signal can be obtained by a signal corresponding to the magnetic pole position of the magnet roller 4. Coaxially with magnet roller 4,
Signals can be obtained by providing a signal generating disk corresponding to the magnetic pole position and combining it with a fixed sensor. For example, a configuration can be applied in which the signal disk is an optical disk consisting of a transparent part and an opaque part, and a photoelectric sensor generates the signal. As another signal generating device, a Hall element may be fixedly provided corresponding to the end of the magnet roller, and the magnetic pole position of the magnet roller may be detected by the Hall element. The signal obtained by the above-mentioned magnetic pole position detector is applied to the sampling signal circuit 47, and is obtained when the non-spilled portion between the magnetic poles passes in front of the toner concentration detection device 12. The sampling circuit 46 is operated to sample only the detection signal. And shaping circuit 4
4, control signal generation circuit 45, reference voltage generation circuit 4
3. For the determination circuit 48, etc., the circuit used in FIG. 6 is used as is.

FIG. 8 is a configuration diagram of an embodiment in which a DC bias is applied to the transparent plate 16 constituting the detection window of the toner concentration detection device 12. A conductive treatment layer 17 is formed on the surface of the transparent plate 16 facing the developer 20, and a bias having the same polarity as the toner polarity is applied between the conductivity treatment layer 17 and the sleeve 5 via a bias power supply 18. This is how it was done. This generates an electrostatic repulsion force between the transparent plate 16 and the toner particles, making it possible to more effectively prevent toner from adhering to the transparent plate 16. The applied voltage in this case is at least
It is desirable that the voltage is 50V or higher.

Although the present invention has been described in detail using embodiments above, the present invention is not limited to these embodiments, and can be modified within the scope of the invention by applying other known signal processing circuits. It is. For example, in the above example, the control signal generation circuit turns on/off the toner supply device.
Although the driving signal is generated, it is also possible to display the measured value of toner concentration or to generate a duty driving signal for the toner replenishing device.

As explained above, the present invention is arranged such that when the magnetic pole portion of the magnet roller passes in front of the detection window of the toner concentration detection device, the spikes of developer on the sleeve come into contact with the transparent plate of the detection window. The detection window is cleaned and the detection window can be maintained in a constant clean state at all times, and the reflectance of the area between the magnetic roller magnetic poles and the intermediate area where the developer is uniformly and densely arranged is improved. Since it is detected, a high-level detection signal with little noise can be obtained, and it is possible to always perform stable and highly accurate toner concentration detection.

[Brief explanation of drawings]

FIG. 1 is a diagrammatic cross-sectional view showing the configuration of an example of a developing device equipped with a toner concentration detection device according to the present invention;
FIG. 2 is a diagram showing the distribution of developer on the developing roller, FIGS. 3a and 3b are sectional views showing the configuration of an example of the toner concentration detection device according to the present invention, and FIG. 4 is a diagram showing the toner concentration detection device according to the present invention. A diagram showing the output of a photodetector when the density detection device is used, FIG. 5 is a block diagram showing an example of the control circuit of the toner density detection device according to the present invention, and FIG. 6 is a diagram showing the control circuit in the present invention. FIG. 7 is a block diagram showing the configuration of still another embodiment of the control circuit according to the present invention, and FIG. 8 is a block diagram showing the configuration of still another embodiment of the control circuit according to the present invention. FIG. 7 is a diagram showing the configuration of another embodiment. DESCRIPTION OF SYMBOLS 1...Developing device, 2...Housing, 3...Developing roller, 4...Magnetic roller, 5...Sleeve, 6...Bear height regulation plate, 7...Scraper, 8
...Agitator, 9...Toner supply hopper, 10...
...Toner supply roller, 11... Vibration plate, 12...
Toner concentration detection device, 13... Light source, 14... Photodetector, 15... Element block, 16... Transparent plate, 17... Conductive treatment layer, 18... Bias power supply, 20... Developer, 21 ...Charge carrier, 41
... Amplification circuit, 42 ... Voltage comparison sampling circuit, 43 ... Reference voltage generation circuit, 44 ... Shaping circuit, 45 ... Control signal generation circuit, 46 ... Sampling circuit, 47 ... Sampling signal circuit, 4
8... Judgment circuit, 49... Magnetic pole position detector.

Claims (1)

[Claims] 1. In a device for detecting toner concentration in a developer in a magnetic brush developing device that performs development using a dry two-component developer using a developing roller having a sleeve made of a non-magnetic material and a magnetic roller disposed inside the developing roller, A light source that emits light toward the developer, a photodetector that receives light reflected from the developer, and a raised portion of the developer that is located in front of the light source and the photodetector, facing the developing roller. A transparent plate arranged at a distance so as to be in contact but not in contact with a portion where no spikes are formed; a means for rotating the magnet roller; an optical toner comprising means for determining the reflectance of the developer based on a signal output from the photodetector when a portion passes through the front surface of the transparent plate to detect the toner concentration. Concentration detection device.