JP2007199364A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of restoring an image forming operation earlier after resumption of toner supply while preventing occurrence of toner fog. <P>SOLUTION: When the image forming apparatus is allowed to resume toner supply from the state in which the toner concentration is below a predetermined target level (1.25[V] in FIG. 2) resulting from non-supply of toner to a developing unit, the supply of toner to the developing unit is controlled so that the toner concentration is maintained at a predetermined restoring level (1.00[V] in FIG. 2) lower than the target level. Thereafter, the restoring level is gradually increased to the target level at predetermined intervals, for example, each time the number of sheets subjected to image formation reaches a predetermined value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus used for a copying machine, a printer, a facsimile, a plate making system, and the like, and more particularly to toner replenishment control thereof.

  As high-speed and high-quality image forming apparatuses, copying machines and laser beam printers employing an electrophotographic system are known. In the image forming process in such an image forming apparatus, first, the charged photosensitive member is exposed based on image information to be output, and an electrostatic latent image that is a set of minute dots is formed. The Thereafter, in the developing device, the electrostatic latent image is visualized using a developer containing toner and a carrier, and the image is transferred to a sheet as a transfer material by the transfer device.

  The conventional image forming apparatus detects that the toner container is empty (toner container empty) based on a decrease in toner density in the developing unit, and further detects that the toner density has decreased. There are also models in which the image forming operation of the apparatus is forcibly stopped at that time.

  As another conventional technique related to the invention of the present application, for example, in Patent Document 1, a latent image potential is detected from when the toner container is detected until the image forming operation is forcibly stopped. And a technique for changing a potential difference (contrast potential) between a developing bias potential and a developing bias potential to a value smaller than normal.

JP 2001-265102 A

  Certainly, if the image forming apparatus forcibly stops the image forming operation of the apparatus as the toner density in the developing device decreases, the user is encouraged to replace the toner container without continuing low-quality image output. It is possible.

  However, in the conventional image forming apparatus, when the replacement operation with a new toner container is completed in a state where the image forming operation is forcibly stopped, the toner density of the developing device reaches a normal target level. The toner is supplied to the developing device at a time until it reaches the upper limit, and then the image forming operation of the apparatus is restored (empty canceled) (see FIG. 4).

  As described above, in the configuration in which toner is supplied to the developing device at a time, the remaining toner in the developing device and the newly supplied toner are not completely mixed, and the toner density in the developing device is unevenly distributed. Toner fog (a phenomenon in which toner is deposited outside the print area) may occur. For this reason, in the conventional image forming apparatus, it is necessary to perform sufficient stirring in the developing device when supplying toner, and it takes a long time to return to the image forming operation.

  Further, since the toner concentration sensor for detecting the toner concentration in the developing device is not necessarily highly accurate, in the configuration in which the toner is replenished to the developing device all at once to the target level as described above, the toner is likely to be oversupplied. Even if a sufficient stirring time was ensured, there was still a high risk of causing toner fog.

  The prior art disclosed in Patent Document 1 is a technique for avoiding toner fogging when it is between the time when the toner container is empty and the time when the image forming operation is forcibly stopped. Thus, no toner supply control at the time of return from the forced stop state is disclosed or mentioned. The prior art disclosed in Patent Document 1 is a technique for avoiding toner fog by developing bias control, and has an essential configuration different from that of the present invention.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of quickly returning the image forming operation after resuming toner supply while suppressing the occurrence of toner fog.

  In order to achieve the above object, an image forming apparatus according to the present invention comprises a photoconductive image carrier; a charger that uniformly charges the image carrier; and an image exposure of the surface of the image carrier after charging. An exposure unit that forms an electrostatic latent image; a developer that forms a toner image by storing, stirring, and supplying a developer containing toner and a carrier and attaching the toner to the electrostatic latent image; A toner density sensor for detecting the toner density of the developer contained in the developer; a toner container serving as a toner replenishment source for the developer; and maintaining the toner density at a predetermined target level. A toner replenishment control unit for controlling toner replenishment to the developing unit, wherein the toner replenishment control unit does not replenish toner to the developer and the toner density is reduced. From below the target level, When the toner is ready to be replenished, toner replenishment to the developer is controlled so that the toner density is maintained at a predetermined return level lower than the target level. It is set as the structure (1st structure) which raises step by step to the said target level.

  The image forming apparatus having the first configuration includes an empty detection unit that detects the empty state of the toner container based on the detection result of the toner density sensor; and after the empty state of the toner container is detected. Forcibly stopping means for forcibly stopping the image forming operation of the apparatus; based on the detection result of the toner density sensor, detecting that the toner density has reached the return level, and releasing the empty for returning the image forming operation of the apparatus And a means (second structure).

  In the image forming apparatus having the first or second configuration, the toner replenishment control unit increases the return level step by step every time the number of image forming sheets of the device reaches a predetermined value (first step). 3).

  With the image forming apparatus according to the present invention, it is possible to quickly return the image forming operation after resuming toner supply while suppressing the occurrence of toner fog.

  In the following, a case where the present invention is applied to a network compatible digital multi-function peripheral that employs an electrophotographic system and has functions as a scanner, printer, copier, facsimile, etc. will be described as an example.

  FIG. 1 is a vertical sectional front view schematically showing a configuration example of an image forming apparatus according to the present invention.

  As shown in the figure, an image forming apparatus 100 according to the present invention includes a cassette type paper feeding unit 101, a manual paper feeding unit 102, a paper transport unit 103, a document feeding unit 104, an optical unit 105, an image, The image forming apparatus includes a forming unit 106, a transfer unit 107, a fixing unit 108, and a paper discharge tray unit 109. In addition, the solid line arrow in the drawing indicates the conveyance path of the paper P.

  The cassette-type paper feeding unit 101 is a means for stacking and storing paper P (a material to be transferred such as cut paper) before printing, and the paper P is separated and sent out one by one.

  The manual paper feed unit 102 is a means for placing a sheet P of a size that is not in the cassette type paper feed unit 101 or a material to be transferred such as an OHP sheet.

  The paper transport unit 103 is a unit that transports the paper P sent from the cassette type paper feed unit 101 or the manual paper feed unit 102 to the transfer unit 107.

  The document feeding unit 104 is a unit that separates documents on which images such as characters, graphics, and patterns are drawn one by one and conveys them to the optical unit 105.

  The optical unit 105 is a unit that optically reads a document conveyed from the document feeding unit 104, converts the optical signal into an electric signal, and generates desired image data.

  The image forming unit 106 is a unit that forms a toner image on an image carrier (drum) based on image data obtained by the optical unit 105. More specifically, the image forming unit 106 includes a photoconductive image carrier, a charger for uniformly charging the image carrier, and exposing the surface of the image carrier after charging to form an electrostatic latent image. And a developer (a two-component developer in the example of the present embodiment) containing, agitating, and supplying a developer containing toner and a carrier. A developer unit 106a that forms a toner image by attaching the toner, a toner concentration sensor 106b that detects the toner concentration of the developer contained in the developer unit 106a, and a toner container that serves as a toner supply source for the developer unit 106a. (Toner cartridge) 106c. The toner density sensor 106b is configured to output a voltage signal corresponding to the toner density by detecting the magnetism of the toner.

  The transfer unit 107 is a unit that transfers the toner image formed on the image carrier onto the paper P.

  The fixing unit 108 is a unit that heats the paper P carrying an unfixed toner image and fixes the toner image.

  The paper discharge tray unit 109 is a unit that stacks and stores the paper P on which the toner image is fixed.

  When a user copies a document using the image forming apparatus 100 having the above-described configuration, a document on which an image such as a character, graphic, or pattern is drawn is loaded on the document feeding unit 104. The document feeding unit 104 separates the documents one by one and feeds the document, and the optical unit 105 reads the image data. Then, an electrostatic latent image of the original image is created on the image carrier (drum) by the image forming unit 106. A toner image is formed from the electrostatic latent image, and the toner image is transferred by the transfer unit 107 to the pre-printing paper P sent in synchronization by the paper transport unit 103. Thereafter, the paper P carrying the unfixed toner image is sent to the fixing unit 108 and heated by a heat roller to fix the toner image. The paper P discharged from the fixing unit 108 is discharged to a paper discharge tray unit 109 outside the apparatus.

  Although not shown in the drawing, the image forming apparatus 100 according to the present invention includes a control unit (CPU [Central Processing Unit], etc.) that controls each unit of the apparatus in addition to the above-described components, and various information. A display unit for displaying a user, an operation unit for accepting user operations, a memory unit used as a storage area for control programs, a storage area for image data, and a development area, and an information processing apparatus connected via a network Various circuit elements such as a communication unit and a network control unit for establishing a connection with a public telephone line or a modem for performing mutual conversion between image data and a facsimile signal are provided.

  In addition to the function as the overall control unit of the apparatus, the control unit develops from the toner container 106c so as to maintain the toner density at a predetermined target level based on the detection result of the toner density sensor 106b. Based on the function as a toner replenishment control unit for controlling toner replenishment to the container 106a and the detection result of the toner density sensor 106b, it is detected that the toner container 106c is empty (that is, the toner container 106c is empty). Based on the function as an empty detection means, the function as a forced stop means for forcibly stopping the image forming operation of the apparatus after the empty of the toner container 106c is detected, and the detection result of the toner density sensor 106b, An empty that detects that the specified return level has been reached and returns the image forming operation of the device. Functions as a sustained means are provided.

  Next, the toner replenishing operation which is a characteristic part of the present invention will be described in detail with reference to FIG. 2 together with FIG.

  FIG. 2 is a diagram for explaining a toner replenishing operation according to the present invention. In this figure, the vertical axis indicates the output voltage (that is, toner density) of the toner density sensor 106b, and the horizontal axis indicates the passage of time (number of images formed).

  At time t1, when the toner container 106c becomes empty (out of toner), it becomes impossible to continue supplying toner to the developing device 106a. Therefore, after time t1, the toner density of the developing device 106a decreases from the target level (1.25 [V] in FIG. 2) every time an image forming operation is performed.

  Thereafter, the image forming operation is continued, and at time t2, when the toner density decreases to a predetermined lower limit level (1.00 [V] in FIG. 2), the control unit of the image forming apparatus 100 causes the empty of the toner container 106c. Is detected.

  Further, at time t3, when the number of image forming sheets after the detection of empty reaches a predetermined value (for example, 100 sheets), the control unit of the image forming apparatus 100 considers that the remaining amount of toner is small and performs the image forming operation. Forcibly stop. Such forced stop control can prompt the user to replace the toner container 106c without continuing low-quality image output.

  Thereafter, when the replacement operation for the new toner container 106c is completed at time t4, the control unit of the image forming apparatus 100 sets the toner density to a predetermined value lower than the above-described target level (1.25 [V]). The toner supply to the developing device 106a is controlled so as to maintain the return level (1.00 [V] in FIG. 2).

  When the toner density reaches a predetermined return level at time t5, the control unit of the image forming apparatus 100 returns (empty cancels) the image forming operation of the apparatus that has been in the forced stop state. Thereafter, the control unit of the image forming apparatus 100 starts from the toner container 106c to the developing unit so as to maintain the toner density at the current return level until the number of images formed after the return reaches a predetermined value (for example, 100). The toner supply to 106a is controlled.

  At time t6, when the number of image formations after the return reaches a predetermined value, the control unit of the image forming apparatus 100 increases the return level to a return level one level higher (1.05 [V] in FIG. 2). Thereafter, toner supply from the toner container 106c to the developing device 106a is controlled so that the toner density is maintained at the current return level until the number of formed images after the level transition reaches a predetermined value (for example, 100). To do.

  Thereafter, the control unit of the image forming apparatus 100 gradually increases the return level to a final target level at a predetermined interval, that is, every time the number of image formed sheets reaches a predetermined value.

  In the case of FIG. 2, at time t7, time t8, time t9, and time t10, the return levels are 1.05 → 1.10 [V], 1.10 → 1.15 [V], respectively. 1.15 → 1.20 [V] and 1.20 → 1.25 [V].

  As described above, when the image forming apparatus 100 according to the present invention is not able to replenish the toner to the developing device 106a and the toner density falls below a predetermined target level, the image forming apparatus 100 can be replenished with toner. A configuration in which toner supply to the developing device 106a is controlled so as to maintain the toner density at a predetermined return level lower than the target level, and thereafter the return level is gradually increased to the target level at predetermined intervals. It is said that.

  More specifically, according to the embodiment, the image forming apparatus 100 according to the present invention has a return level (1.00 [V]) in which the toner density is lower than the normal target level (1.25 [V]). ), The toner supply operation is once completed, and then the residual difference (0.25 [V]) between the target level and the return level is increased in five stages, that is, 0.05. The current return level is increased by [V].

  By adopting such a configuration, it is possible to avoid excessive toner replenishment and mixing failure compared to the conventional configuration in which toner is replenished to the developing device at one time until the toner density reaches the target level at normal times. Can do. Therefore, with the image forming apparatus 100 according to the present invention, the image forming operation can be returned early after the replenishment of toner while suppressing the occurrence of toner fog. Also, with the image forming apparatus 100 according to the present invention, unlike the prior art disclosed in Patent Document 1, the above-described effects can be achieved by controlling the toner supply amount without requiring development bias control. .

  Next, the stepwise control of the return level among the above-described toner replenishing operations will be described in more detail with reference to FIG.

  FIG. 3 is a flowchart for explaining the toner replenishing operation according to the present invention (corresponding to the operation after time t4 in FIG. 2).

  When the replacement operation for the new toner container 106c is completed at time t4 in FIG. 2, in step S1, an initial setting for stepwise control of the return level is performed. The initial settings include the final value X of the return level (that is, the target level of the toner density in the steady state), the initial value of the return level (X−N), the number of steps M of the return level, and the current step. The number S is defined. For example, according to FIG. 2, in step S1, X = 1.25 [V], (X−N) = 1.00 [V] (ie, N = 0.25 [V]), M = 5, and , S = 0 are defined respectively.

  Thereafter, in step S2, it is determined whether or not the output level (that is, toner density) of the toner density sensor 106b has reached the initial value (X−N) = 1.00 [V] of the return level. Here, when it is determined that the toner density has not reached the initial value of the return level, the toner is replenished in step S3, and the determination is repeated. On the other hand, if it is determined that the toner density has reached the initial value of the return level, the flow proceeds to step S4.

  If it is determined in step S2 that the toner density has reached the initial value of the return level, in step S4, the image forming operation of the apparatus that has been in the forced stop state is returned (empty cancelled) (FIG. 2). Equivalent to time t5). When the empty state is canceled, the error state of the display panel or the like is canceled, and the apparatus is returned to the image formable state (ready state).

  After the empty is canceled in step S4, in the subsequent step S5, it is determined whether or not the toner density is maintained at the current return level (that is, (X−N) + (N / M) × S). If it is determined that the toner density is not maintained at the current return level, toner is replenished in step S6, and the determination is repeated. On the other hand, if it is determined that the toner density is maintained at the current return level, the flow proceeds to step S7. Note that immediately after the empty is released, the current step number S is defined as 0, so the current return level is (X−N) = 1.00 [V] (the same value as the initial value of the return level).

  If it is determined in step S5 that the toner density is maintained at the current return level, in step S7, it is determined whether or not the current return level should be stepped up. For example, the number of formed images is set to a predetermined value. A determination is made whether or not it has been reached. If it is determined that the current return level should not be stepped up, the flow is returned to step S5, and the toner density maintenance determination is continued. On the other hand, if it is determined that the current return level should be stepped up, the flow proceeds to step S8.

  If it is determined in step S7 that the current return level should be stepped up, in step S8, the current step number S is incremented by one (S ← S + 1). For example, at time t6 in FIG.

  After the count-up in step S8, in the subsequent step S9, it is determined whether or not the current step number S exceeds the final step number M. If it is determined that the current step number S does not exceed the final step number M, the flow is returned to step S5, and the toner density maintenance determination is continued based on the new return level. Is done. On the other hand, when it is determined that the current step number S exceeds the final step number M, the series of processes described above is terminated.

  For example, at time t6 in FIG. 2, the current step number S (= 1) does not exceed the final step number M (= 5), so the flow returns to step S5. At this time, the new return level is (X−N) + (N / M) × 1 = 1.05 [V]. Also at time t10 in FIG. 2, since the current step number S (= 5) does not exceed the final step number M (= 5), the flow is returned to step S5. At this time, the new return level is (X−N) + (N / M) × 5 = 1.25 [V] (normal target level). On the other hand, after time t10 in FIG. 2, it is determined in step S5 that the toner density has reached the normal target level, and in step S7, the number of images formed after the return level transition has reached a predetermined value. In step S8, the step number S is counted up to six. As a result, in step S9, the current step number S (= 6) exceeds the final step number M (= 5). Therefore, the above series of processing ends.

  In the above embodiment, the case where the present invention is applied to a network-compatible digital multifunction peripheral has been described as an example. However, the scope of application of the present invention is not limited to this, and a printing function and a copying function are described. The present invention can also be widely applied to an image forming apparatus provided with only each.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  For example, in the above embodiment, the case where the empty of the toner container 106c is detected and the toner supply is restarted from the state where the image forming operation of the apparatus is forcibly stopped has been described as an example. The application opportunity is not limited to this, and when the toner container 106c is replaced in the period from when the toner container 106c becomes empty until the empty is detected (so-called toner low period). Also, it is possible to perform the same control as described above. Referring to FIG. 2, when the toner container 106c becomes empty and, for example, the toner container 106c is replaced when the toner density falls below 1.10 [V], toner supply is resumed. At this time, the toner may be gradually supplied in the same manner as before, such as 1.10 [V] → 1.15 [V] → 1.20 [V] → 1.25 [V].

  The present invention is a technique suitable for an image forming apparatus such as a scanner, a printer, a copier, a facsimile, or a digital multifunction machine having these functions. It is.

FIG. 2 is a vertical sectional front view schematically showing a configuration example of an image forming apparatus according to the present invention. FIG. 4 is a view for explaining a toner replenishing operation according to the present invention. These are flowcharts for explaining a toner replenishing operation according to the present invention. FIG. 10 is a diagram for explaining a conventional example of a toner replenishing operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Cassette type paper feeding part 102 Manual paper feeding part 103 Paper conveying part 104 Document feeding part 105 Optical part 106 Image forming part 106a Developer 106b Toner density sensor 106c Toner container (toner cartridge)
107 Transfer section 108 Fixing section 109 Paper discharge tray section P Paper (material to be transferred)

Claims (3)

  A photoconductive image carrier; a charger that uniformly charges the image carrier; an exposure device that forms an electrostatic latent image by exposing the surface of the image carrier after charging; and a toner and a carrier A developer that stores, stirs, and supplies the developer and attaches toner to the electrostatic latent image to form a toner image; and detects the toner concentration of the developer contained in the developer A toner concentration sensor; a toner container serving as a toner supply source for the developer; and a toner supply controller for controlling toner supply to the developer so as to maintain the toner density at a predetermined target level; The toner replenishment control unit includes a state in which toner replenishment can be performed again from a state in which the toner density is below a predetermined target level without performing toner replenishment to the developer. The toner concentration The toner supply to the developer is controlled so as to maintain a predetermined return level lower than the target level, and thereafter, the return level is gradually increased to the target level at predetermined intervals. Image forming apparatus.   Empty detection means for detecting the empty state of the toner container based on the detection result of the toner density sensor; forcibly stopping means for forcibly stopping the image forming operation of the apparatus after the empty state of the toner container is detected; And an empty canceling means for detecting that the toner density has reached the return level based on the detection result of the toner density sensor and returning the image forming operation of the apparatus. Item 2. The image forming apparatus according to Item 1.   3. The image forming apparatus according to claim 1, wherein the toner replenishment control unit increases the return level step by step every time the number of images formed by the apparatus reaches a predetermined value.

Images