JP2808108B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer using an electrophotographic system, and more particularly to an image forming apparatus capable of forming a multicolor image. (Prior Art) Conventionally, in an image forming apparatus using an electrophotographic method, a charging potential of a photosensitive drum, a developing bias potential applied to a developing device, and the like are adjusted in order to keep a density of a formed image constant. Image forming conditions such as a development contrast potential and a fog prevention potential have been controlled. In particular, in a multi-color copying machine, image forming conditions are set according to the characteristics of the developer for each color so that the density for each color is substantially the same. (Problems to be Solved by the Invention) However, in such a conventional example, although the image forming conditions for each color of the developer are adjusted, a change in image density due to a change in the environment where the developer is placed is performed. Is not taken into account. Particularly, the change in image density due to the change in humidity is remarkable, and the density difference is conspicuous because the rate of change in density due to moisture absorption differs for each color of the developer, that is, depending on the type. There was a point. Therefore, a humidity sensor for measuring an environmental change in the vicinity of the developing device is provided in order to obtain the amount of absorbed moisture of the developer, and the image forming condition is changed by the control means according to the detection result of the sensor for a certain period of time and the type of the developer. Although measures are conceivable, at the beginning of use, such as immediately after repairing the equipment, there is not enough data for environmental measurement, or inappropriate data has been input, so the image forming conditions must be adjusted to appropriate values. However, the above-mentioned problem that the density cannot be set and the density change or the density difference occurs cannot be solved. Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and the object of the present invention is not only to form an image having an appropriate density at the time of normal image formation, but also to detect an environment such as immediately after device repair. It is an object of the present invention to provide an image forming apparatus capable of forming an image having an appropriate density even when a result is not accurately obtained. (Means for Solving the Problems) In order to achieve the above object, in an image forming apparatus according to the present invention, an image forming means for forming an image on a photoconductor using a developer, and detecting humidity. Detecting means, storing means for storing a history of outputs of the detecting means at a plurality of timings within a predetermined time in the past, and estimating a moisture absorption state of the developer according to a plurality of data stored in the storing means; Control means for controlling image forming conditions relating to the image density of the image forming means according to the moisture absorption state. Also, the apparatus has input means for rewriting data stored in the storage means, and when the plurality of data for the predetermined time is not stored in the storage means, the control means is detected by the detection means. The latest output may be stored in the storage unit as data for the predetermined time, and then the image forming condition may be controlled based on the data rewritten by the input unit. Further, the image forming means may include a charger for charging the photoconductor, and the control means may control a grid voltage of the charger. (Operation) According to the present invention having the above configuration, the storage unit stores the history of the humidity at a plurality of timings in the past predetermined time, and the control unit controls the moisture absorption of the developer according to the plurality of stored data. By estimating the state and controlling the image forming conditions relating to the image density according to the moisture absorption state, not only the current humidity but also whether the humidity is changing in the direction of increasing or decreasing. Thus, the image can be formed under image forming conditions suitable for the current moisture absorption state of the developer, so that a high-quality image with a proper density can always be formed. Also, the apparatus has input means for rewriting data stored in the storage means, and when the plurality of data for the predetermined time is not stored in the storage means, the control means is detected by the detection means. The latest output is stored in the storage unit as data for the predetermined time, and then the image forming conditions are controlled based on the data rewritten by the input unit. The image forming condition can be set to an appropriate value even when it is insufficient or incorrect. (Example) Hereinafter, the present invention will be described based on an illustrated example. FIG. 2 is a block diagram showing an embodiment of the image forming apparatus according to the present invention. In FIG. 2, reference numeral 1 denotes a rotary developing device, and a yellow developing device 1Y and a magenta developing device
Equipped with 1M, cyan developing unit 1C and black developing unit 1BK. 2 is a developer (toner) replenishing device for the developing device 1, 2Y is a yellow hopper, 2M is a magenta hopper, 2C
Indicates a cyan hopper, and 2BK indicates a black hopper. Regarding the operation of the entire color image forming apparatus, first,
The case of the full color mode will be briefly described as an example. 3
Is a photosensitive drum rotating in the direction of the arrow shown in the figure, and the photosensitive member on the drum 3 is uniformly charged by the charger 4. Next, image exposure is performed by a laser beam E modulated by a yellow image signal of a document (not shown), an electrostatic latent image is formed on the photosensitive drum 3, and after that, the electrostatic latent image is fixed in advance to a developing position. The development is performed by the yellow developing device 1Y. Here, the rotary developing device 1 and the charger 4 constitute an image forming unit. On the other hand, the transfer paper that has advanced via the paper feed guide 5a, the paper feed roller 6, and the paper feed guide 5b is held by the gripper 7 in synchronization with a predetermined timing, and is electrostatically moved by the contact roller 8 and its opposite pole. Is wound around the transfer drum 9. The transfer drum 9 rotates in the direction of the arrow shown in FIG. 1 in synchronization with the photosensitive drum 3, and the developed image developed by the yellow developing device 1Y is transferred by the transfer charger 10 in the transfer section.
The transfer drum 9 continues to rotate as it is, and the next color (first
Prepare for the transfer of magenta in the figure. On the other hand, the photosensitive drum 3 is discharged by the charger 11 and
It is cleaned by the cleaning member 12, is charged again by the charger 4, and is exposed by the next magenta image signal in the same manner as described above. During this time, the developing device 1 rotates, and the magenta developing device 1M is fixed at a predetermined developing position and performs a predetermined magenta development. Subsequently, the same process as described above is performed for cyan and black, respectively, and when the transfer for four colors is completed, the four-color visual image on the transfer paper is discharged by the chargers 13 and 14, and the gripper 7 is removed. At the same time, the sheet is separated from the transfer drum 9 by the separation claw 15 and sent to the fixing device 17 by the conveyor belt 16 to complete a series of full-color printing operations, thereby forming a full-color print image. Further, in the present embodiment, in addition to the above-described configuration, an environment sensor 19 as a detection unit including a humidity sensor and a temperature sensor is provided at a position where the moisture absorption of the toner is well reflected, such as near the toner hopper or near the developing device. Equipped. FIG. 1 is a block diagram showing one embodiment of the present invention.
4a is a high-voltage power supply for supplying power to the primary charger, 4b is a grid bias power supply for supplying power to the grid for controlling the amount of charge applied to the drum 3 to a desired value, and 1 'is provided for the developing device. A power supply for supplying a developing bias in which a DC component is superimposed on the AC waveform, and a control means 18 such as a microcomputer for controlling the output value of each power supply. Control means
The reference numeral 18 is connected to an environment sensor 19 and a potential sensor 20, and is also connected to a humidity data input unit 21 and a memory 22 as a storage unit. The operation of this embodiment will be described below. Figure 3 is a graph showing the relationship between the grid bias voltage surface potential (horizontal axis) and the photosensitive drum 3 (the vertical axis), corresponding to the surface potential when in FIG, V _D is not the light irradiation, Y _L corresponds to the surface potential when irradiated with light. From the figure, the surface potential V _D That charge quantity Come to only a range (use range) is proportional to the grid bias V _G. Further, there is a surface potential V _L is also similar tendency after light irradiation, the grid bias V ratio i.e. proportional coefficient of variation with respect to the amount of change in _G is V _D than atmospheric (alpha case it is V _L in the case of> beta ). Therefore, before performing the print sequence, the control means 18 measures each of V _D and V _L by the preset grid voltages V _G1 and V _G2 with the potential sensor 20 and, based on each data, the grid voltage as shown in FIG. _Suppose the charging curves of V _D and V _{L with} respect to the change of. Then, actually from the charging curve obtained by the above operation at the time of image formation, image contrast i.e. difference or V _D -V _L between the surface potential V _L after DC component and the light irradiation of the developing bias described below A grid voltage that has a predetermined value is obtained by calculation, and the grid bias power supply 4b is controlled. Further portions corresponding to the white image, for the case reversal development of this embodiment, obtains the developing bias lower constant than V _D so that the toner in a portion corresponding to V _D does not adhere potential value (V _B) developing The bias power supply 1 'is controlled. FIG. 4 is a graph showing the effect of image density on humidity when printing is performed under the same image forming conditions. As shown in FIG. 4, under the same image forming conditions, the lower the humidity, the lower the density and the higher the humidity. As the concentration increases, the concentration increases. Therefore, if the humidity is detected, the contrast potential V _cont corresponding to the humidity is obtained, and the image forming conditions are set based on the value, it is possible to obtain a stable image regardless of changes in environmental conditions. Become. Further, as shown in the figure, since the density with respect to the humidity differs for each color, if the image forming conditions are varied for each color, the difference in the image density due to the difference in the color of the developer can also be corrected. . Hereinafter, the operation of this embodiment will be specifically described based on the flowcharts shown in FIGS. 5 (a), (b), (c) and (d). First, the process A will be described with reference to FIG. In the interrupt processing or the like, the temperature and the humidity are measured by the environment sensor 19, for example, once every 30 minutes or several times during 30 minutes, and the average value is measured. For example, the average value is stored in the buffer area of the memory 22 for 8 hours. deep. In the step, the absolute humidity or a value corresponding thereto (for example, a mixing ratio) is calculated based on the data.
This is because the image density is considered to be proportional to the absolute humidity, that is, the amount of water in the air. In the step, it is determined whether or not the calculation of the absolute humidity (mixing ratio) has been performed for 8 hours, and after the calculation has been performed for 8 hours, the average values x, y, and z for 2 hours, 4 hours, and 8 hours are obtained in the step. . These average values x, y, and z are used as the variables at the time of contrast calculation by performing the following condition determination. In the step, 2 hour average x
Is determined whether the mixture ratio is 16.5 g or more. If it is 16.5 g or more, the flag is set to CONT1. This is determined that the high humidity state has continued for 2 hours or more. Next, in step, the current value
It is determined whether it is 16.5g or more. If it is 16.5g or more, the flag is set to CONT2. This was determined to be low humidity for 2 hours, but it is now time to go to high humidity. Next in step 8
It is determined whether the average value z of the time is 9 g or more, and if it is 9 g or more, the flag is set to CONT3. Thereby, the humidity is assumed to be in a moderate humidity state for 8 hours or more. Next, in step, compare whether the 4-hour average y is 9g or more, and if it is 9g or more, flag
Change to CONT4. Thus, it is determined that the vehicle is moving from low humidity to medium humidity. Then, if other than the above, that is, if the 4-hour average value is <9 g, the flag is set to CONT5 with the low humidity state. Incidentally, the above processing is performed because the speed of moisture absorption and dehumidification of toner is different when going from low humidity to high humidity and when going from high humidity to low humidity. That is, although the image density is proportional to the absolute humidity, it is determined not by the humidity of the atmosphere but by the amount of moisture absorbed by the toner. Next, in a step, a variable H for contrast calculation is determined by the contrast flag. This is, for example, cont
In the case of 1, since the humidity is completely adjusted to a high humidity, the variable is a 2-hour average value x. In the case of CONT2, since the state is intermediate between the low humidity and the high humidity, the average value (x + w) / 2 of the 2-hour average value x and the current value w is obtained. In addition, memory with contrast flags and color information
Search and read out the coefficients of the calculation formula from the table in 22.
The general formula of the calculation is the contrast potential V _cont = a ₁ −b ₁ H, where H is the above-mentioned variable and a ₁ and b ₁ are coefficients. The contrast potential V is obtained from the coefficients and variables obtained above.
Calculate _cont and store in memory in steps. The above is repeated for four colors for each color. FIG. 6 is a plot of the above calculation formula. Since the coefficient is changed for each color as shown in the figure, it is possible to absorb and correct the difference in density change for each color as shown in FIG. Next, the processing B will be described with reference to FIG. First, the photosensitive drum is rotated and the primary high-voltage power supply 4a is turned on as in the normal copy sequence. Then step in to the grid bias to a predetermined value V _G1 to measure the surface potential V _D1 of the photosensitive drum is stored in memory. Next, in step irradiated with the drum by the maximum amount of light illuminates the laser is stored in the surface potential V _L1 after light irradiation was measured memory. Further, the storing step, in then measuring the surface potential V _L2 by the grid bias Another to a predetermined value V _G2 and the laser is turned OFF in each memory measure the surface potential V _D2 in step. As a result, measurement data for calculation described later is obtained. Laser ON / OFF sequence, V _G1 , V _G2
May be changed according to the convenience of the sequence. Further, the processing A and the processing B are independent of each other, and whichever is performed first and the timing of the processing does not have to be simultaneous. Next, the process C will be described with reference to FIG. Process C must always be performed after processes A and B have been performed. First, in steps, _VG1 , _VG2 and measurement data _VD1 , _VD2 , V
_L1, the inclination of each of the charging curve from V _L2 V _D and V _L alpha,
β and α−β are calculated according to the following equations. Then read the contrast voltage V _cont calculated by the fog removal voltage V _B described above are stored in the buffer area processing A in step. Then, the grid bias V _G at step is determined to a voltage sum of the V _cont and V _B are obtained. That is, the following calculation is performed. Step by calculation then V _D If Motomare grid voltage. V _D = α (V _G −V _G1 ) + V _D1 Further, the development bias DC component (DB) is determined in steps. DB = V _D -V _B above processing in steps the process terminates is determined to have finished for four colors. Grid bias control values V _G, the developing bias control values DB obtained by the above. The above calculation is repeated for each color to obtain V _G and DB for four colors. Since the grid bias and the developing bias obtained as described above take into account the environmental conditions and the differences with respect to the environmental conditions for each color, an extremely stable image having an appropriate density can be obtained. By the way, as described above, in the present invention, the history of humidity is a factor that determines image forming conditions. Therefore, it is necessary to collect temperature and humidity data by energizing at all times. However, for example, at the time of installation or when the environmental sensor fails, no data exists in the buffer area or data different from the actual data is contained. For this reason, for example, immediately after repair, proper image forming conditions cannot be obtained unless some processing is performed in advance in the service mode. Therefore, the following processing as shown in FIG. That is, first, immediately after the power is turned on in the step, the temperature and the humidity are measured, and in the step, the temperature and the humidity are stored in the entire 8-hour buffer area of the memory assuming that the temperature and the humidity have continued as a steady state. Then, the above-described processes A, B, and C are performed in a step, an image sample is collected in a normal copy sequence in a step, and the image density is checked in a step. Here, when the image is not in the proper density, for example, when the
The time data includes data in a high humidity state, and the contrast is determined according to the data. However, the toner put into the machine at the time of installation is adjusted to the moisture content of the environment sealed at the time of shipment from the factory, and thus may be completely different from the environment at the time of installation. Therefore, step,
When the image density is not in the proper state, the humidity data can be collectively rewritten by the input means 21 by a key switch or the like in the service mode. The humidity data rewriting means 21 uses, for example, two keys so that one switch rewrites the data value to the low humidity side and the other switch rewrites the data value to the high humidity side. Then, a value which becomes humidity data corresponding to one contrast each time the switch is pressed is added to or subtracted from the humidity data. By performing the initial setting by such processing, a proper image can be obtained from the beginning. Moreover, as time passes, temperature and humidity data are accumulated, and an appropriate image can always be obtained. In the above embodiment, the apparatus capable of forming a multi-color image has been described. However, the present invention is not limited to this, and can be applied to a normal single-color image forming apparatus. Further, in the above embodiment, the case where the environment detecting means measures the absolute humidity has been described. However, it is also possible to control the image density by measuring factors that affect the developer other than the humidity such as the temperature. Further, in the above embodiment, the case where the image forming condition is determined by the charging potential on the photosensitive drum, the potential after light irradiation, and the developing bias potential has been described. However, other conditions such as the charging potential of the developer are controlled. You may. (Effects of the Invention) The present invention has the above-described structure and operation, and stores a history of humidity at a plurality of timings within a predetermined time in the past, and absorbs moisture of a developer according to a plurality of stored data. By estimating the state and controlling the image forming conditions related to the image density according to the moisture absorption state, not only the current humidity but also whether the humidity is increasing or decreasing. Thus, the image can be formed under image forming conditions suitable for the current moisture absorption state of the developer, so that a high-quality image with a proper density can always be formed. Also, the control means has input means for rewriting data stored in the storage means, and when the storage means does not store a plurality of data for a predetermined time, the control means determines a latest output detected by the detection means in a predetermined manner. Since the image forming condition is controlled based on the data rewritten by the input unit after being stored in the storage unit as data for the time, when the storage content of the storage unit is insufficient or inaccurate, for example, immediately after the device is repaired. Also, the image forming condition can be set to an appropriate value. Therefore, there is an effect that an image having an appropriate density can always be formed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a block diagram of the embodiment, FIG. 3 is a diagram showing grid bias voltage and drum surface potential. A graph showing the relationship,
FIG. 4 is a graph showing a change in density of the developer with respect to humidity for each color, and FIGS. 5 (a), (b), (c) and (d) show the procedure for setting image forming conditions in the embodiment. FIG. 6 is a flowchart showing the relationship between the set contrast potential and the humidity. Description of reference numerals 1 ... Developing unit (developing unit) 3 ... Photoreceptor drum 4 ... Primary charger (charging unit) 18 ... Control unit 19 ... Environmental sensor (detecting unit) 21 ... Input unit 22 ... Memory (storage means)

Claims (1)

(57) [Claims] An image forming means for forming an image on the photoreceptor using a developer; a detecting means for detecting humidity; a storing means for storing a history of outputs of the detecting means at a plurality of timings within a predetermined time in the past; Control means for estimating the moisture absorption state of the developer according to the plurality of data stored in the storage means, and controlling image forming conditions relating to the image density of the image forming means according to the moisture absorption state; Image forming apparatus. 2. An input unit for rewriting data stored in the storage unit, and when the storage unit does not store a plurality of data for the predetermined time, the control unit includes:
The latest output detected by the detection means is stored in the storage means as data for the predetermined time, and then the image forming condition is controlled based on the data rewritten by the input means. Range 1
An image forming apparatus according to any one of the preceding claims. 3. 2. An image forming apparatus according to claim 1, wherein said image forming means has a charger for charging said photosensitive member, and said control means controls a grid voltage of said charger.