JPH0361947B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an image density control device in a recording apparatus. [Prior Art] A recording device that visualizes a latent image formed on a latent image carrier using a two-component developer containing toner and carrier, such as an electronic copying machine, an electrostatic recording device,
Alternatively, various printers are well known in the art. When such a two-component developer is used, the toner is consumed sequentially, so the toner concentration of the developer
That is, the ratio (weight ratio or volume ratio) of toner to carrier gradually decreases, and the image density (reflection density) of the visible image decreases accordingly. Therefore, an image density control device that forms a standard latent image on a latent image carrier, detects the density of the standard image obtained by developing this image, and replenishes toner to the developer of the developing device according to this has conventionally been used. It is more used. By using such a control device, it is possible to prevent the image density from becoming too high or too low, and it becomes possible to obtain an image of constant quality. However, this type of control device had the following problems. The image density of a visible image also changes due to various causes other than the toner density of the developer. For example, in an electronic copying machine that has a latent image bearing member made of a photoreceptor and a charger that charges the latent image carrier before forming a latent image, if the shield or coronode of the charger becomes dirty, the charging potential on the surface of the photoreceptor decreases. change,
When this potential decreases, the image density of the visible image decreases even if the toner concentration itself of the developer does not change.
At this time, the image density control device operates to compensate for this decrease in image density, and the toner density of the developer is increased. A similar development occurs when the carrier in the developer deteriorates. Conversely, if the lenses, mirrors, etc. of the exposure optical system that exposes the photoreceptor become dirty, the amount of light directed to the photoreceptor decreases, and the image density of the visible image increases. Therefore, at this time, the image density control device operates to lower the toner density of the developer in order to keep the image density constant. In this way, when attempting to maintain the image density itself at a desired level, the toner density itself may fluctuate due to changes in various elements in the copying machine or the characteristics of the developer. If the change in toner density does not become particularly excessive, there is no particular problem because the image density itself is maintained at the desired level, but if this change becomes noticeable and the toner density becomes extremely high. If this happens, the toner adhering to the carrier will separate from the carrier, scattering outside the developing device, and contaminating the inside of the copying machine. On the other hand, if the toner concentration becomes too low, carrier particles in the developer may adhere to the photoreceptor during the developing operation and may damage the photoreceptor. Such problems also occur in recording devices other than electronic copying machines. [Problems to be Solved by the Invention] An object of the present invention is to provide an image density control device for a recording apparatus that eliminates the above-mentioned conventional drawbacks. [Means for Solving the Problems] In order to achieve the above object, the present invention includes a standard latent image forming means for forming a standard latent image on a latent image carrier;
a developing device that develops the formed standard latent image with a two-component developer to form a standard image; an image density detection means that detects the density of the formed standard image; a toner concentration detection means for detecting the toner concentration of the two-component developer by detecting a characteristic value of the two-component developer; and a toner concentration detection means for detecting the toner concentration of the two-component developer; toner concentration control means for controlling the toner concentration of the two-component developer by controlling the toner supply amount; a setting means for setting at least one of an upper limit value or a lower limit value of the detection result of the toner concentration detection means; When the setting means is an upper limit setting means, when the detection result of the toner density detection means reaches or exceeds the upper limit value, toner replenishment is prohibited regardless of the detection result of the image density detection means, and the setting When the means is a lower limit setting means, the control means includes a control means for replenishing toner regardless of the detection result of the image density detection means when the detection result of the toner density detection means reaches or falls below the lower limit value. This paper proposes an image density control device for a printing apparatus. [Embodiment] Hereinafter, a specific example in which the present invention is applied to an image density control device for an electronic copying machine will be described, and the drawbacks of the conventional technology will be explained in more detail with reference to the drawings. FIG. 1 shows an example of such an electronic copying machine, and first the overall structure and operation thereof will be explained. A latent image carrier configured as a drum-shaped photoreceptor 1 is supported on the frame of the copying machine, and the photoreceptor 1 is driven to rotate clockwise as a copying operation begins.
At this time, the surface of the photoreceptor is charged to a predetermined polarity by a charger 2 having a coronode 3 and a shield 4. On the other hand, an original 7 held down by a pressure plate 6 is placed on a contact glass 5 provided at the top of the copying machine, and this original 7 is illuminated by a light source lamp 8 moving in the direction of arrow A. The light from the original 7 is transmitted through a first mirror 9 that moves together with a lamp 8, and second and third mirrors 10 and 1 that move in the direction of arrow B.
After being reflected at 1, it passes through the lens 12,
The light is then reflected by the fixed fourth mirror 13 and reaches the charged surface of the photoreceptor 1, on which the image of the document 7 is formed. In this way, an electrostatic latent image corresponding to the image of the original is formed on the surface of the photoreceptor, and this latent image is transferred to the developing device 14 (see also FIG. 3).
as it passes through the toner, it is visualized by the toner. This visible image is transferred onto a transfer paper 16 fed from a paper feeder 15 to the photoreceptor 1 by the action of a transfer charger 17. The transfer paper 16 is then separated from the photoreceptor 1 by a separation charger 18, passes through a fixing device 19, at which time the transferred visible image is fixed on the transfer paper, and is then discharged out of the main body of the copying machine. The toner remaining on the surface of the photoreceptor after the transfer of the visible image is cleaned by the cleaning device 20.
After cleaning, the surface of the photoreceptor is subjected to a static neutralizing action by a static neutralizing charger. As shown in FIG. 2a, the portion preceding the latent image formation area X formed during each copying operation becomes a non-image area Y. As clearly shown in FIG. 3, the developing device 14 in this example has a tank 22 containing a two-component developer 23 having toner and a carrier. In this example, the carrier of the developer 23 is made of a magnetic material, and the toner is made of non-magnetic material. A developing sleeve 24 is disposed inside the tank 22 and is positioned opposite to the photoconductor 1 and to which a bias voltage is applied as necessary. A magnet 25 is disposed within the sleeve 24 . The developer 23 in the tank 22 is stirred by the stirring blade 2.
6. The sleeve 24 rotates counterclockwise, or the magnet 25 installed therein rotates clockwise,
Alternatively, the developer 2 may be rotated together.
The developer is carried counterclockwise while being carried on the surface of the sleeve 24, and the amount of developer carried is regulated by the doctor 27. The regulated developer reaches the opposing area D between the photoreceptor 1 and the sleeve 24, where the toner in the developer electrostatically transfers to the latent image on the photoreceptor.
The latent image is visualized. The excess developer scraped off by the doctor 27 flows on the guide plate 28, falls to the bottom of the tank 22 again, and is stirred by the stirring blade 26.
In this way, the developer 23 in the tank 22 circulates while being subjected to an agitation action. As the copying operation is performed as described above, the toner in the developer 23 is sequentially consumed, so the toner concentration of the developer in the tank gradually decreases. In order to compensate for this, toner 30 in a toner container 29 attached to the developing device 14 is replenished into the developer of the developing device 14 in a manner described later. In this example, a toner supply roller 31 is rotatably supported at the lower opening of the toner container 29, and as the roller rotates, toner is supplied into the tank 22 through a groove 32 formed on its surface. The amount of toner fed from the toner container 29 into the tank 22 is controlled by the image density control device according to the present invention as follows. In FIG. 1, a reference member 34 having a predetermined standard reflection density is provided on the surface 33 of the contact glass 5 at a position adjacent to the contact glass 5. Prior to this, the surface 33 of the reference member 34 is illuminated by the lamp 8, which is imaged onto the non-image area Y of the photoreceptor 1 by the aforementioned imaging optical system, just as in the case of a normal copying operation. be done. At this time, since the non-image area Y is also charged by the charging charger 2, this area has a standard latent image 35 (FIG. 2a) with a surface potential corresponding to the density of the surface 33 of the reference member 34.
is formed, and this standard latent image 35 is visualized by the toner of the two-component developer 30 in the developing device 14. This is the standard image 35a (FIG. 2b). As described above, in this example, the standard latent image forming means for forming a standard latent image on the latent image carrier is formed by the reference member 34, the charging charger 2, and the imaging optical system including the lamp 8. The standard latent image is composed of
The image is developed with a two-component developer in the developing device 14 used during normal copying operations, and a standard image is formed. The standard image 35a is controlled to have an image density that corresponds to the toner density of the developer contained in the tank 22. In other words, this type of copying machine is generally configured so that the operator can adjust the density of the copied image by operating a scale (not shown) provided on the operation section, but it is not possible to set the density to any desired density. The density of the standard image is not affected by this setting. For example, if the operator operates the scale to change the bias voltage applied to the sleeve 24 of the developing device 14, thereby changing the density of the visible image,
No matter how the operator sets the scale, a constant predetermined bias voltage is applied to the sleeve 24 when the standard latent image is visualized. Since the density on the surface of the reference member 34 is constant, the density of the obtained standard image 35a is substantially always determined by the toner density of the developer 23. When the standard image 35a formed as described above passes through the developing device 14, the light emitting element 37 of the image density detection means 36 shown in FIG. Element 38
incident on . The output of the light receiving element 38 becomes a voltage corresponding to the density of the standard image 35a, and the replenishment of toner in the toner container 29 is controlled in accordance with this. FIG. 4 shows a standard image 3 formed on the photoreceptor 1.
The above-described image density detection means 3 for detecting the density of 5a
6 and a block diagram showing an example of a configuration related thereto, the detection means 36 includes a resistor 3 that divides the power supply voltage Vc.c. in addition to a light emitting element 37 and a light receiving element 38.
9 and 40, and a comparator 41 that compares the divided voltage and the voltage of the light receiving element 38.
The output is supplied to a drive circuit 42 that drives the toner supply roller 31 (FIG. 3). Two switch circuits 43 and 44 are connected to the line that supplies the output of the comparator 41 to the drive circuit 42, which will be described later. The standard image 35a is the light emitting and light receiving elements 37, 38
When the light-emitting element 37 emits light, the light-receiving element 38 outputs a voltage corresponding to the density of the standard image.
is compared with a reference voltage obtained by dividing the power supply Vc.c. by resistors 39 and 40, and it is determined whether the density of the standard image is lower or higher than the density corresponding to the reference voltage. Now, when the density of the standard image is lower than the density corresponding to the reference voltage, the comparator 41 generates a high potential output, and this high potential output is supplied to the drive circuit 42 via switch circuits 43 and 44 to replenish toner. Drive the roller 31. Therefore, the toner 30 in the toner container 29 is supplied to the tank 22, and the toner 30 in the toner container 29 is supplied to the tank 22.
The toner concentration within the container is increased. Further, when the density of the standard image is equal to or higher than the density corresponding to the reference voltage, the comparator 41 generates a low potential output, and this low potential output is transmitted to the switch circuits 43 and 44.
The toner replenishment roller 31 is supplied to the drive circuit 42 via the toner replenishment roller 31, and the toner replenishment to the tank 22 is stopped. This operation is performed each time the light emitting element 37 emits light as the photoreceptor 1 rotates so that the standard image faces the light emitting and light receiving elements 37 and 38. Therefore, by appropriately setting the reference voltage, The toner density of the developer 23 can be adjusted so that the image density of the visible image obtained from the original image can be maintained at approximately a predetermined value. As described above, in this example, the drive circuit 42 and the toner replenishment roller 31 control the amount of toner replenishment to the developing device 14 based on the detection result of the image density detection means 36, and It constitutes a toner concentration control means for controlling the toner concentration of the component-based developer 23. Note that the standard image 35a is the light emitting/light receiving elements 37, 3.
8 and reaches the transfer charger 17, the transfer paper has not yet been sent to the position of the charger 17, so there is no inconvenience that the standard image is transferred to the transfer paper. Further, this standard image is also cleaned by the cleaning device 20, and the surface of the photoreceptor after cleaning is subjected to the static eliminating action by the static eliminating charger 21 in the same way as a normal latent image. The above control operation can be performed every time a copying operation is performed, but the amount of developer 23 in the tank 22 is large, and there is a time delay in changes in toner concentration even with toner consumption and replenishment. In order to reduce the load on the cleaning device 20 and to avoid consuming a large amount of toner adhering to the standard latent image 35, the density of the standard image is detected every 10 copy operations, for example. It is also possible to perform it once. At this time, the non-image area Y shown in FIG. 2a is not charged by the charger 2, or even if this is done,
Before forming a latent image of the original image, erase light L (Fig. 1,
3), the non-image area Y is neutralized. Further, the output from the comparator 41 when the image density is detected is held for a period until the next image density is detected, and toner replenishment is continued or prohibited during this period. It can also be configured. Such an operation can be performed by adding a holding circuit. For example, a flip-flop circuit (see FIG. (not shown) is inserted between the comparator 41 and the switch circuit 43, and the comparator 41
The toner replenishment output (high potential output) from the toner replenishment output (high potential output) can be maintained for a predetermined period of time. With the configuration described above, even if the toner is sequentially consumed in the developing device 14, the image density can be maintained at approximately a predetermined value. However, as explained earlier, changes in image density are not necessarily caused only by changes in toner density, and therefore, if only the image density is controlled, there is a risk that the various inconveniences mentioned above will occur. be. This will be explained in more detail with reference to the drawings. When the coronode 3 and shield 4 of the charging charger 2 shown in FIG. 1 become contaminated, the charging current changes, and the charging potential on the surface of the photoreceptor changes. As a result, the density of the standard image 35a changes, and if only the image density control described above is performed, the toner density of the developer 23 contained in the developing device 14 changes. That is, if the surface potential of the photoconductor 1 decreases, the image density decreases, and therefore the toner concentration of the developer 23 increases, and conversely, if the surface potential of the photoconductor 1 increases, the toner concentration decreases. In order to reduce the effects of dirt on the charger 2, it has been known to make the output of the power supply constant current, but even if this is done, if the coronode 3 becomes locally dirty, this dirt will This causes uneven charging on the photoreceptor. If such charging unevenness occurs in the area where the standard latent image 35 is formed and the potential of the latent image 35 decreases, the density of the standard image decreases and the toner concentration of the developer 23 increases. In addition, the charging potential on the surface of the photoreceptor changes due to temperature drift of the high source voltage for the charging charger 2, drift over time, or changes in corona discharge development due to fluctuations in temperature, humidity, and atmospheric pressure. Developer 23
Toner density fluctuates. In extreme cases, if the power supply for the charger 2 breaks down and its output drops significantly, the surface potential of the photoreceptor will drop significantly, and the density of the standard image will also drop significantly. There is a risk that the concentration of In addition to the dirt on the optical element and the deterioration of the carrier described above, the sleeve 2 in the developing device 14
The image density of the visible image also changes due to fluctuations in the bias voltage to 4, deterioration of the surface of the photoreceptor 1, dirt on the surface 33 of the reference member 34, discoloration, etc. Concentration changes. When such changes become significant and the toner concentration becomes too high, toner scattering becomes severe, and when it becomes too low, carrier particles adhere to the surface of the photoreceptor during the developing operation, and the cleaning device 20 removes the carrier particles from the photoreceptor. This causes inconveniences such as being rubbed against the body surface and causing scratches on the surface. When toner scattering becomes significant, the various elements of the copying machine become more contaminated, and as a result, there is a risk that the toner concentration will further increase, resulting in a repeat of the vicious cycle. When the inside of a copying machine becomes extremely dirty, it takes a lot of time to clean it and return it to normal condition. Furthermore, if the light emitting element 37 and light receiving element 38 of the image density detection means 36 become dirty with scattered toner, the image density detection function itself is degraded. In order to eliminate the above-mentioned disadvantages, the image density control device according to the present invention includes a two-component developing device disposed in the developing device, as illustrated in FIG. It has a toner concentration detection means 45 that detects the toner concentration of the developer by detecting the characteristic value of the developer, and by this means 45 and the setting and control means described later, the The toner concentration of the developer 23 is prevented from becoming extremely high or extremely low. The details will be explained below. The toner concentration detection means 45 shown as an example in FIG. 4 includes a toner concentration detection coil 46, a variable inductance 47 for adjusting the oscillation frequency connected in series with the coil 46, and a series circuit connected in parallel with these. , a capacitor 48 forming a resonant circuit together with the coil 46 and the variable inductance 47.
and an oscillator consisting of inverters 49 and 50. Such toner concentration detection means 45
The output is outputted via an inverter 51 as a buffer. The coil 46 is connected to the tank 22 in the developing device 14.
(FIG. 3), and in this example, as shown in FIG. A portion of the developer wound around the portion 53a and moving on the guide plate 28 falls from the hole 52, and the developer passes through the coil 46. Since the developer carrier is made of a magnetic material and the toner is made of a non-magnetic material, the amount of magnetic material in the coil 46 changes according to changes in the toner concentration of the developer passing through the coil 46, and its magnetic permeability changes. Therefore, the inductance of the coil 46 changes. Therefore, the resonant frequency of the resonant circuit configured together with the capacitor 48 changes, and the oscillation frequency of the toner concentration detection means 45 changes. The relationship between the toner concentration and the oscillation frequency of the toner concentration detection means 45 exhibits a characteristic as shown in FIG. 5, for example. In this way, by detecting the characteristic values of the two-component developer 23 in the developing device 14, the toner concentration of this developer can be detected. Toner concentration detection means 45 corresponding to toner concentration
The output, that is, the oscillation output of the frequency corresponding to the toner concentration, is sent to the frequency-voltage converter 5 via the inverter 51.
4 and is converted into a voltage. The output voltage of frequency-to-voltage converter 54 is supplied to comparators 55 and 56. Further, the comparator 55 is supplied with the voltage _E1 to its non-inverting input terminal, and is configured to generate a negative voltage output when the output voltage of the frequency-voltage converter 54 exceeds the voltage _E1 . . On the other hand, the comparator 56 has a voltage E ₂ (E ₁ >
E ₂ ) and is configured to generate a negative voltage output when the output voltage of the frequency-to-voltage converter 54 falls below voltage E ₂ . Further, in the line that supplies the output of the comparator 41 to the drive circuit 42, there is a switch circuit 43 which is switched by the output of the comparator 55, and a switch circuit which is cascade-connected to the comparator 55 and which is switched by the output of the comparator 56. The switch circuit 43 is turned off by the output when the input of the comparator 55 is higher than the voltage E ₁ , and the switch circuit 44 has the input of the comparator 56 set to the voltage E _{2 .}
When the output drops further, the circuit changes to voltage source 57.
The drive circuit 42 is configured to supply the output of the drive circuit 42 to the drive circuit 42. As the developer 23 in the tank 22 shown in FIG. 3 passes through the coil 46, the toner concentration detection means 45 outputs an output at a frequency corresponding to the toner concentration of the developer 23, as shown in FIG. It has occurred. This oscillation output of the toner concentration detection means 45 is sent to a frequency voltage converter 54 and a buffer inverter 5.
1, the output of the frequency-voltage converter 54 becomes a voltage output at a level corresponding to the toner concentration. This output voltage is determined by comparators 55 and 56.
and are compared with voltages E ₁ and E ₂ .
Now, the output voltage of the frequency voltage converter 54 is
When it is lower than E ₁ , the output voltage of the comparator 55 becomes a high potential, the switch circuit 43 is turned on, and the output voltage of the comparator 41 is guided to the switch circuit 44 . Conversely, when the output voltage of the frequency voltage converter 54 exceeds the voltage _E1 , the comparator 55
The output voltage of the comparator 41 becomes a low potential and the switch circuit 43 is turned off, and the output voltage of the comparator 41 is cut off by the switch circuit 43. Further, when the output voltage of the frequency-voltage converter 54 exceeds the voltage _E2 , the output of the comparator 56 becomes a high potential output, the switch circuit 44 becomes the contact position shown in FIG. 4, and the output of the switch circuit 43 becomes to the toner replenishment drive circuit 42, and the output voltage of the frequency-voltage converter 54 becomes the voltage E ₂
In the following cases, the output of the comparator 56 becomes a low potential output, and the switch circuit 44 switches to supply the voltage of the voltage source 57 to the toner supply drive circuit 42. Therefore, the relationship between toner density, standard image density, and toner replenishment is as shown in Table 1. In Table 1, the toner concentration is indicated by the output voltage E of the frequency-voltage converter 54.

[Table] When the toner supply control is performed as described above, the toner concentration changes as shown in FIG. 6. When the toner concentration of the developer 23 reaches the upper limit concentration determined by the voltage _E Toner replenishment is stopped regardless of the image density, and is limited as shown in section H in FIG. 6 (therefore, in this section H, the image density of the visible image may fall below a predetermined value). . When the toner density of the developer 23 reaches the lower limit density determined by the voltage _E2 , the toner replenishing roller 31 is rotated by the voltage of the voltage source 57 and toner is replenished into the tank 22, regardless of whether the image density is high or low ( Therefore, in this case, the image density may be higher than the predetermined height). When the toner density is between the voltages E ₁ and E ₂ , toner replenishment is controlled according to the density of the standard image as described above, and a predetermined image density is obtained. As described above, although the image density may deviate from a predetermined value, the toner density never exceeds the density corresponding to the voltage _E1 , and stains due to toner scattering are suppressed. Also, the toner density will not decrease below the density corresponding to the voltage E ₂ ,
Therefore, the inconvenience of the surface of the photoreceptor 1 being damaged by the carrier is suppressed. According to experiments, the upper limit of the toner concentration was set at approximately 5.5% by weight for the carrier, and the lower limit of the toner concentration was set at approximately 5.5% by weight for the carrier.
When the amount of toner was set at about 1.5% by weight relative to about 98.5% by weight of the carrier, it was possible to prevent significant toner scattering and significant adhesion of the carrier to the photoreceptor. In the above embodiment, priority is given to detecting the upper limit value or lower limit value of toner density than to detecting image density, and when the toner density reaches the upper limit value or lower limit value, regardless of the image density, toner replenishment or Since this is configured to stop, even if image density detection is performed once for a plurality of copying operations, there will be no inconvenience such as the toner density exceeding the upper limit or lower limit. Furthermore, since there is a relatively large range between the upper limit and the lower limit, it is not possible to adjust the image density in response to the fluctuations, except when there are large fluctuations in the characteristics of the copying machine elements or developer. Therefore, a situation in which the toner density reaches the upper limit value or the lower limit value and the image density of the visible image exceeds a predetermined value does not usually occur at an early stage, causing inconvenience in the use of the copying machine. There are almost no Furthermore, in the above-described embodiment, a case has been described in which the control of the toner density based on the density of the standard image is limited by both the upper limit value and the lower limit value of the detection result of the toner density detection means 45. Depending on the replenishment speed, etc., it may be sufficient to limit either the upper limit or the lower limit. At that time, when the toner concentration becomes high and the inside of the copying machine is contaminated with toner, it takes a long time to clean it.
Since the toner concentration generally tends to increase over time, it is desirable to control only the upper limit value. What has been described above can be similarly applied to the embodiment described later with reference to FIG. As described above, when the setting means sets at least one of the upper limit value or the lower limit value of the detection result of the toner concentration detection means, and the setting means is the upper limit setting means, the detection result of the toner concentration detection means is the upper limit value. When the value does not reach or exceeds this value, toner replenishment is prohibited regardless of the detection result of the image density detection means, and when the setting means is a lower limit setting means,
An example of a control means is configured for replenishing toner regardless of the detection result of the image density detection means when the detection result of the toner density detection means reaches or falls below the lower limit value. By the way, as explained in detail above, the image density of a visible image changes due to changes in the various elements of the copying machine or the characteristics of the developer, but if you can know the changes in these characteristics, It becomes possible to adjust elements whose characteristics have changed. At that time, if the image density of the visible image is kept at a predetermined level,
The change in the above characteristics approximately corresponds to the change in toner concentration. Therefore, if the toner concentration can be known, it becomes possible to know changes in the characteristics of the elements of the copying machine. From this point of view, in the embodiment shown in FIG. 4, a voltmeter 58 is provided to measure the output voltage of the frequency-voltage converter 54, and the toner concentration is displayed by the voltmeter 58. concentration corresponding to voltage E ₁ or E ₂ ,
Or when the density is close to this, it can be determined that various elements of the copying machine or characteristics of the developer need to be adjusted. In this case, it is not displayed which element of the copying machine is causing the toner density to become too high or too low, but the characteristics of some elements change in the direction of increasing toner density, and the elements change in the direction of lowering it. Since the elements are known in advance,
If the toner concentration can be known, it is possible to roughly judge which element's characteristics are changing, and therefore it is possible to make adjustments in a short time.
If such adjustments are made during maintenance and inspection of the copying machine,
Almost any copying machine can be kept under the best conditions. Furthermore, due to manufacturing variations in each element of individual copying machines, there are some that have a particularly strong tendency to increase the toner concentration, and others that have a particularly strong tendency to lower the toner concentration. ,
As described above, if the tendency of each element can be grasped by knowing the toner concentration, the element can be adjusted in accordance with the tendency. For example, if it is possible to know from changes in toner density that the charging current of a certain copying machine's charging charger tends to decrease relatively early, then when making adjustments,
By adjusting the charging current to be high in advance within a range that does not cause any inconvenience, it is possible to lengthen the time until an excessive increase in toner concentration occurs due to a decrease in the current over time. In this way,
Each element can be adjusted to suit the unique characteristics of each copying machine. Further, the configuration in which changes in characteristics of each element are known by displaying toner concentration can be applied to cases other than the configuration in which upper and lower limit values of toner concentration are set. The basic embodiments of the present invention have been described above, but
The present invention can be constructed by variously modifying the above specific examples. For example, in the embodiment shown in FIG. 4, the setting means for setting the upper limit and lower limit of the detection result of the toner concentration detection means 45 is constituted by a frequency voltage converter 54 and comparators 55 and 56, and the toner concentration is A control means for controlling toner replenishment and prohibition when the detection result does not reach or exceeds the lower limit value or upper limit value is constituted by switch circuits 43, 44 and a drive circuit 42, but a microcontroller is used to control the copying machine. When a computer is used, the functions of comparators 55, 56, frequency-voltage converter 54, and switch circuits 43, 44 shown in FIG. 4 can be performed by a microcomputer. In the configuration shown in FIG. 7, the comparator 4 in the image density detection means 36
The output of step 1, that is, binary information indicating whether the density of the standard image is lower or higher than a predetermined density, is read into the microcomputer 59 that constitutes the control section, and the read data is held in memory until the next reading. As will be described later, toner replenishment control is performed based on a combination of the held data and the toner concentration detection data. On the other hand, the output of the oscillator in the toner concentration detection means 45 is buffered by the inverter 51 and input to the event counter terminal _T1 of the microcomputer 59. In this case, the output of the oscillator can be input directly to the microcomputer by using a computer 59 that has an internal counter that counts external events and can start and stop the counter, read data, etc. using a program. . If such a function is provided, the means for detecting toner concentration can be constructed with a small number of parts, resulting in low cost. In the case of a microcomputer that does not have a built-in event counter, by providing an external counter and controlling its operation with the microcomputer,
Similarly, toner concentration can be detected. The computer determines whether the frequency f _H corresponding to the upper limit of toner density is exceeded, or between the frequencies f _L and f H corresponding to the lower limit, as shown in Figure 5, according to a program written in the ROM in _advance . Is it in
Alternatively, it is determined whether the oscillation frequency is lower than f _L . Image density data and oscillation frequency in this case,
In other words, the relationship between the toner concentration data and the toner replenishment signal is summarized as shown in Table 2 below.

〔Effect of the invention〕

According to the image density control device according to the present invention, it is possible to prevent the toner concentration of the two-component developer contained in the developing device from becoming extremely high or low, and to prevent the toner from scattering outside the developing device. Alternatively, the problem of the carrier adhering to the surface of the latent image carrier can be reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory sectional view of an electrophotographic copying machine, Fig. 2 a and b are schematic perspective views of a photoreceptor, Fig. 3 is a sectional view of a developing device, and Fig. 4 is a block diagram showing an embodiment of the present invention. 5 is a graph showing the characteristics of the toner concentration detection means, FIG. 6 is a graph showing an example of the relationship between the toner density and the number of copies, and FIG. 7 is a block similar to FIG. 4 showing another embodiment. It is a diagram. 14...Developing device, 23...Two-component developer,
30...Toner, 35...Standard latent image, 35a...
Standard image, 45...Toner density detection means.

Claims (1)

[Claims] 1. A standard latent image forming means for forming a standard latent image on a latent image carrier, a developing device for developing the formed standard latent image with a two-component developer to form a standard image, an image density detection means for detecting the density of a standard image; and a toner density disposed in the developing device for detecting the toner density of the two-component developer by detecting a characteristic value of the two-component developer. a detection means; a toner concentration control means for controlling the toner concentration of the two-component developer by controlling the amount of toner supplied to the developing device based on the detection result of the image density detection means; and the toner concentration detection means. a setting means for setting at least one of an upper limit value or a lower limit value of the detection result of the toner concentration detection means, and when the setting means is an upper limit setting means, the detection result of the toner concentration detection means reaches or exceeds the upper limit value; When toner replenishment is prohibited regardless of the detection result of the image density detection means, and when the setting means is a lower limit setting means, when the detection result of the toner density detection means reaches or falls below the lower limit value. An image density control device in a recording apparatus, comprising: a control unit for replenishing toner regardless of a detection result of the image density detection unit.