JP2009025378A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which can elongate the service life of the developing roller and prevent the cost increase. <P>SOLUTION: This printer develops the electrostatic latent images formed on the photoreceptor drum by using toner to form images. When detecting that the toner amount is less than the value M1 in the developing chamber (the time c) while performing the print job for forming images on sheets by supplying sheets one by one, it switches the image forming speed from the normal speed to half speed and continues image forming on the remaining sheets while refilling toner in the developing chamber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by developing an electrostatic latent image formed on an image carrier with toner.

  In a developing unit of an image forming apparatus such as a copying machine, a developing roller that rotates in a state where toner is usually carried to visualize an electrostatic latent image on a photosensitive drum, and a stirring roller that stirs toner in the developing chamber A supply roller for conveying the agitated toner and supplying it to the developing roller is provided. In addition, a toner hopper is provided that replenishes the developing chamber with an amount of toner corresponding to the consumed amount of toner when the toner in the developing chamber is consumed as the image is formed.

In such an image forming apparatus, for example, when copying a large amount of a document with a high ratio of the area of the image portion to the total area of one page (hereinafter referred to as “printing ratio”), the amount of toner consumption is large. The toner supply may not be able to keep up.
If such a state continues, the amount of toner in the developing chamber will be less than the amount necessary for development, causing trouble in development. As a method for avoiding this, for example, when the toner supply cannot catch up and the toner in the developing chamber is reduced to a specified amount, the image formation is interrupted, the toner is supplied, and the developing roller is rotated to stir the toner in the developing chamber. However, when the toner is transported and carried on the developing roller and the toner necessary for development is supplied, image formation is resumed.

Patent Document 1 discloses a configuration in which the toner supply amount per unit time is increased by increasing the driving speed of the toner supply roller.
JP 2004-341220 A

  However, in the method of replenishing toner by interrupting the image forming operation as described above, the toner is forcibly stirred and conveyed in the developing chamber separately from the original image formation every time the replenishment time comes. Deterioration due to toner wear easily proceeds due to friction between the toner particles. Deteriorated toner is unlikely to contribute to development and is likely to remain in the developing chamber. Therefore, as the proportion of the deteriorated toner in the developing chamber increases with time, the developing performance is reduced.

Further, it is necessary to drive the developing roller, the agitation roller, and the like other than image formation, which places an extra burden on the drive system and shortens the life.
Furthermore, in the configuration of Patent Document 1, a driving motor having a speed higher than that of the current one must be used, and an increase in cost is inevitable.
The present invention has been made in view of the above problems, and provides an image forming apparatus capable of preventing an increase in cost while improving development performance and extending the life of a driving system such as a developing roller. It is aimed.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that visualizes a latent image formed on an image carrier with toner and then transfers the image onto a sheet to form an image. During the image forming operation, the toner in the developing chamber is conveyed while being agitated and carried on the developing roller, and the developing means for visualizing the latent image on the image carrier and the toner amount in the developing chamber are sequentially detected. The toner replenishment control means for controlling the toner replenishment according to the detection result and adjusting the toner amount in the developing chamber so as to keep the prescribed amount, and the toner replenishment by the toner replenishment control cannot catch up, and the toner amount in the developing chamber has decreased. Image forming control means for controlling the image forming operation to be slower than the prescribed speed when the prescribed amount is not reached.

  In this way, even when toner supply cannot catch up, it is possible to perform toner supply in parallel while performing image formation. Therefore, every time when the toner replenishment time comes, the image forming operation is interrupted for replenishment, and the replenished toner is forcibly agitated and conveyed in the developing chamber and carried on the developing roller. Thus, the development performance can be improved by suppressing the progress of toner deterioration as compared with the prior art, and the life of the drive system such as the developing roller can be extended. Furthermore, it is not necessary to replace the driving motor for the toner replenishing roller with an expensive one, and cost increase can be prevented.

The image forming control means returns the image forming operation to a specified speed when the toner amount in the developing chamber reaches a specified amount during the image forming operation controlled at a low speed.
In this way, image formation can be completed earlier.
Further, the image forming control means, when the printing rate at the time of image formation for the next sheet is a predetermined value or more, and / or when the next image formation for a plurality of sheets is scheduled to be executed continuously, The slowing control is performed.

In this way, productivity efficiency can be further increased.
Further, the image forming apparatus includes a fixing unit that thermally fixes the toner image transferred on the sheet to the sheet. It is also characterized by lowering.
Further, the image forming apparatus includes a fixing unit that thermally fixes the toner image transferred onto the sheet to the sheet. When the image forming control unit performs a control for delaying the toner image, the temperature of the fixing unit is set higher than the temperature at the specified speed. In the case where image formation is performed with the speed lowered to the specified speed, the temperature of the fixing unit is returned to the temperature at the specified speed.

In this way, it is possible to save power while performing fixing at a fixing temperature more suitable for the image forming speed.
In addition, the image forming control unit is configured such that (a) when the continuous operation time of image formation controlled at a slow speed reaches a predetermined time, (b) the number of continuous executions of image formation controlled at a slow speed is a predetermined number of times. (C) at least one of (a) to (c) when the amount of toner in the developing chamber is reduced to an amount that is expected to cause a problem in development during an image forming operation controlled at a slow speed. If one is satisfied, the current image forming operation is temporarily interrupted and toner replenishment is executed.

In this way, it is possible to suppress that the toner amount in the developing chamber is lower than the amount assumed to cause a problem in development.
Further, the image forming control means interrupts the current image formation and replenishes the toner rather than performing a delay control when an image forming job for continuously forming images on a plurality of sheets is being executed. When the forced toner supply for resuming image formation on the remaining sheets can be completed earlier, the forced toner supply is executed instead of the slow control. To do.

In this way, the image forming job can be completed more quickly.
Further, the image forming control unit changes the image forming speed for each sheet according to the image forming execution condition when performing image forming on a plurality of sheets continuously when performing the slowing control. It is characterized by that.
In this way, a more suitable image forming speed can be set for each sheet according to the image forming execution condition, and the image forming can be executed more efficiently.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described using a tandem color digital printer (hereinafter simply referred to as “printer”) as an example.
<First Embodiment>
(Configuration of the entire printer)
FIG. 1 is a diagram illustrating the overall configuration of the printer 10.

  As shown in FIG. 1, the printer 10 includes an image processing unit 11, a feeding unit 12, a fixing unit 13, and a control unit 14, and is connected to a network (for example, a LAN) to be connected to an external terminal device (not shown). When a print (print) job execution instruction is received from (), color image formation consisting of yellow, magenta, cyan and black colors, or monochrome, for example, black color image formation is executed based on the instruction. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, respectively.

The image processing unit 11 includes image forming units 21Y to 21K corresponding to Y to K colors, an intermediate transfer belt 22, and toner hoppers 25Y to 25K that store toner for supplementing Y to K colors.
The image forming unit 21Y includes a photosensitive drum 1, a charging roller 2 disposed around the photosensitive drum 1, an exposure unit 3, a developing device 4, a primary transfer roller 5, a cleaner 6 for cleaning the photosensitive drum 3, and the like. A Y-color toner image is formed on the photosensitive drum 1. This is the same for the other image forming units 21M to 21K. In the figure, the reference numerals are omitted.

The intermediate transfer belt 22 is an endless belt, is stretched around a driving roller 23 and a driven roller 24, and is driven to circulate in the direction of the arrow in FIG.
The toner hopper 25Y includes a replenishing roller 26 and a stirring roller 27, and supplies Y toner to the developing device 4 of the image forming unit 21Y according to an instruction from the control unit 14. Here, the agitation roller 27 is a member for agitating the contained toner, and the replenishment roller 26 is a member for conveying the agitated toner to the developing device 4.

  FIG. 2 is a schematic view when the toner hopper 25Y and the developing device 4 are connected as seen from the direction of arrow A in FIG. As shown in the drawing, the toner hopper 25Y and the developing device 4 are connected by a cylindrical connecting member 29 at a position on the back side of the apparatus, and the toner conveyed by the replenishing roller 26 passes through the connecting member 29. The developing device 4 is replenished. This is the same for the other toner hoppers 25M to 25K.

  Returning to FIG. 1, the feeding unit 12 feeds a sheet feeding cassette 31 that stores recording sheets (hereinafter referred to as “sheet S”) and a sheet S in the sheet feeding cassette 31 one by one onto the conveyance path 30. A feed roller 32, a transport roller pair 33 for transporting the fed sheet S, a timing roller pair 34 for timing to feed the transported sheet S to the secondary transfer position 351, a secondary transfer roller 35, and the like. I have.

The fixing unit 13 includes a fixing roller 15, a pressure roller 16 that presses against the fixing roller 15 to secure a fixing nip, a temperature detection sensor 17 that detects a surface temperature of the fixing roller 15, and a heater 18 that heats the fixing roller 15. I have.
The control unit 14 drives the exposure unit 3 of the image forming units 21Y to 21K based on an image signal from an external terminal device. For each image forming unit, the exposure unit 3 emits laser light, and the photosensitive drum 1 is exposed and scanned line by line in accordance with a predetermined pixel clock frequency. Before this exposure scanning, the photosensitive drum 1 is uniformly charged by the charging roller 2, and an electrostatic latent image is formed on the photosensitive drum 1 by the exposure scanning of the laser beam.

  The formed electrostatic latent image is developed (visualized) by the developing device 4 to form a toner image on the photosensitive drum 1. The toner images of the respective colors are primarily transferred sequentially onto the intermediate transfer belt 22 by electrostatic force acting between the primary transfer roller 5 and the photosensitive drum 1. At this time, the image forming operations for the respective colors are executed at different timings so that the toner images are superimposed and transferred at the same position on the intermediate transfer belt 22. The color toner images superimposed on the intermediate transfer belt 22 are moved to the secondary transfer position 351 by the circulation drive of the intermediate transfer belt 22.

  The sheet S is fed from the feeding unit 12 via the timing roller pair 34 in accordance with the timing of the image forming operation, and the sheet S is connected to the intermediate transfer belt 22 that is circulated and driven. It is sandwiched between the next transfer rollers 35 and conveyed. At this time, the toner images on the intermediate transfer belt 22 are collectively transferred onto the sheet S by the electrostatic force acting between the secondary transfer roller 35 and the driving roller 23.

The sheet S that has passed through the secondary transfer position 351 is conveyed to the fixing unit 13, and the toner image is heated and pressed when passing through the fixing nip secured by the fixing roller 15 and the pressure roller 16, thereby the sheet S. Then, the toner is discharged through a discharge roller pair 36.
In the above description, the case of executing a color job for forming a color image has been described. However, when executing a monochrome job for forming an image of only a black color, only the image forming unit 21K among the image forming units 21Y to 21K. Is driven, the photosensitive drum 1 of the image forming units 21Y to 21C and the intermediate transfer belt 22 are relatively separated from each other, and the driving of the image forming units 21Y to 21C is stopped.

In the printer 1, a main motor 51, a color developing motor 52, a monochrome developing motor 53, a fixing motor 54, and toner replenishing motors 55 and 56 are arranged.
The main motor 51 rotationally drives the photosensitive drum 1, the intermediate transfer belt 22, the feeding roller 32, the timing roller pair 34, the secondary transfer roller 35, and the like.
The color developing motor 52 rotationally drives each roller such as a developing roller 61 (see FIG. 3) disposed in each developing device 4 of the image forming units 21Y to 21C. The monochrome developing motor 53 rotates and drives each roller arranged in the developing device 4 of the image forming unit 21K.

The fixing motor 54 rotationally drives the fixing roller 15 and the pressure roller 16 of the fixing unit 13.
The toner replenishing motor 55 rotates the replenishing roller 26 and the agitation roller 27 of each of the toner hoppers 25Y and 25M. Here, when the toner replenishing motor 55 rotates forward, the driving force is transmitted only to the toner hopper 25Y (not transmitted to the toner hopper 25M), and the replenishing roller 26 and the stirring roller 27 of the toner hopper 25Y are rotationally driven. On the other hand, when the rotation is reversed, the driving force is transmitted only to the toner hopper 25M, and the supply roller 26 and the agitation roller 27 of the toner hopper 25M are rotationally driven. In such a configuration, for example, a one-way clutch that transmits only the rotational driving force in the forward rotation direction is connected to the supply roller 26 and the agitation roller 27 of the toner hopper 25Y, and another one-way clutch that transmits only the rotational driving force in the reverse rotation direction is connected to the toner hopper 25M. This is realized by connecting to the replenishing roller 26 and the stirring roller 27. The two toner hoppers 25Y and 25M share one toner supply motor 55, thereby reducing the cost.

The toner replenishing motor 56 rotationally drives the replenishing roller 26 and the stirring roller 27 of the toner hoppers 25C and 25K, respectively. The configuration in which the driving force is transmitted to one hopper by switching between forward and reverse rotation is the same as in the case of the toner replenishing motor 55.
(Configuration of developing device 4)
FIG. 3 is a cross-sectional view showing the configuration of the developing device 4.

  As shown in the drawing, the developing device 4 includes a housing 60, a developing roller 61, a supply roller 62, a stirring roller 63, a regulating blade 64, a toner detection sensor 65, and the like. A housing 60 as an example of a developing chamber is filled with toner 68 as a developer. The developing roller 61, the supply roller 62, and the stirring roller 63 are rotatably held in the housing 60, and the developing device 4 for Y to C colors receives the driving force of the color developing motor 52 and is used for K color. The developing device 4 receives the driving force of the monochrome developing motor 53 and rotates in the direction of the arrow in FIG.

  The developing roller 61 is disposed to face the photosensitive drum 1 and carries the toner 68 and conveys it to the developing position 69. The toner 68 on the developing roller 61 moves to the exposed portion on the photosensitive drum 1 at the developing position 69, whereby the toner image is developed on the photosensitive drum 1 (the electrostatic latent image is visualized). ) As the developing roller 61, for example, a thin core resin layer having a predetermined resistance value on a metal core can be used. This thin resin layer is provided mainly for supporting the toner 68 on the surface of the developing roller 61.

The supply roller 62 is disposed to face the developing roller 61, contacts the surface of the developing roller 61, rotates in the counter direction with respect to the developing roller 61, and supplies the toner 68 in the housing 60 to the developing roller 61. As the supply roller 62, for example, a metal roller surface with a foaming elastic member attached thereto can be used.
The regulating blade 64 is arranged so that the tip thereof has a predetermined gap with the surface of the developing roller 61, regulates the amount of toner passing through the gap, and forms a uniform thin layer of toner 68 on the developing roller 61. Let it form. The stirring roller 63 stirs the toner 68 in the housing 60 to prevent the toner 68 from solidifying and retains fluidity.

A replenishing port 66 for receiving replenishing toner from the corresponding toner hopper through the connecting member 29 (FIG. 2) is provided at the upper part of the housing 60, and the toner 68 in the housing 60 is consumed by development. Then, the toner 68 is supplied through the supply port 66.
In the housing 60, the developing roller 61 to the stirring roller 63 rotate simultaneously during the image forming operation, so that the toner 68 moves from the stirring roller 63 through the supply roller 62 along the arrow (thick line) in FIG. After development, the toner is circulated and conveyed by a route such as returning from the developing roller 61 to the stirring roller 63 via the supply roller 62. A portion 67 of the housing 60 that is curved outward along the stirring roller 63 stores a certain amount of toner for supply to the supply roller 62 in an area formed between the housing 60 and the stirring roller 63. It functions as a buffer part. Hereinafter, it is referred to as a buffer unit 67.

  The toner detection sensor 65 is a transmissive optical sensor having a light emitting unit 651 and a light receiving unit 652, and is disposed on the inner wall of the housing 60 and in the vicinity of the buffer unit 67, and detects the amount of toner. Specifically, among the light emitted from the light emitting unit 651, the amount of light received by the light receiving unit 652 varies depending on the amount per unit volume of toner particles passing through the gap between the light emitting unit 651 and the light receiving unit 652. Is output to the control unit 14 as a detection signal indicating the toner amount of the buffer unit 67.

The control unit 14 detects the toner amount in the buffer unit 67 based on the detection signal. For example, toner amount conversion information indicating a correlation between the actual toner amount X [gram] in the buffer unit 67 and the detection signal value Y [volt] detected at that time is obtained in advance through experiments, and the information is obtained. , The current amount of toner existing in the buffer unit 67 can be grasped.
(Configuration of control unit 14)
FIG. 4 is a block diagram illustrating a configuration of the control unit 14.

As shown in the figure, the control unit 14 includes a CPU 141, a communication interface (I / F) unit 142, a ROM 143, a RAM 144, an image forming speed switching unit 145, and a motor driving unit 146 as main components. Each unit can exchange data with each other.
The communication I / F unit 142 is an interface for connecting to a LAN such as a LAN card or a LAN board.

  The image forming speed switching unit 145 executes an image forming speed switching process for switching the image forming speed between the system speed (specified speed) and the reduced speed (half the speed in the present embodiment). Here, the image forming speed means the peripheral speed of the photosensitive drum 3 (speed equal to the conveying speed of the sheet S). Hereinafter, the system speed is referred to as normal speed, and the half speed is referred to as half speed. Details of the image forming speed switching process will be described later.

The CPU 141 reads a necessary program from the ROM 143 and controls the operation of the image processing unit 11 and the like in a unified manner to execute a smooth print job. In addition, the detection signal from the temperature detection sensor 17 of the fixing unit 13 is received, and energization control of the heater 18 is performed so that the temperature of the fixing roller 15 is maintained at a predetermined fixing temperature T0.
Further, for each of the image forming units 21Y to 21K, the detection signal from the toner detection sensor 65 of the image forming unit is received, the toner amount in the buffer unit 67 of the developing device 4 is sequentially detected, and toner is replenished according to the detection result. And the toner replenishment control for adjusting the toner amount in the developing device 4 so as to keep the specified amount is performed.

  In addition, when executing image formation at half speed, the CPU 141 reduces all operation speeds such as image forming, feeding, and fixing in the image processing unit 11 and the feeding unit 12 to half of the normal speed. . Specifically, the main motor 51, the color development motor 52, the monochrome development motor 53, and the fixing motor 54 are controlled at half speed, and a predetermined pixel clock frequency for exposure scanning by the exposure unit 3 is halved. Execute processing such as switching to. The control method is not limited to this as long as it can be executed at half speed.

The ROM 143 stores a control program for executing a print job, a program for executing an image forming speed switching process, the toner amount conversion information, and the like. The RAM 144 is used as a work area when the CPU 141 executes a program.
The motor drive unit 146 switches the rotation speed of the main motor 51 or the like between the normal speed and the half speed according to an instruction from the CPU 141. Specifically, information on the drive current to be supplied to each motor is stored in advance for each of the normal speed and the half speed, and when a half speed instruction is received from the CPU 141, for example, the drive current for the half speed is obtained. Is controlled to rotate at a half speed.

(Contents of image forming speed switching process by control unit 14)
FIG. 5 is a flowchart showing the contents of the image forming speed switching process, and FIG. 6 is a diagram showing the transition of the toner amount due to switching of the image forming speed and toner supply. Here, the flowchart of FIG. 5 is a subroutine for a main routine (not shown). When the processing is completed, the process returns to the main routine. This processing is called in the main routine at every elapse of a predetermined time and executed for each image forming unit during execution of a job in which a plurality of sheets are successively fed and printed as one print job. Is.

  Further, the toner amount reference value M0 shown in FIG. 6 is a value for determining whether or not toner replenishment is necessary, and corresponds to the specified amount. M2 is a value assumed that the toner amount is reduced to such an extent that the development is hindered, and M1 is a value indicating a threshold when the image forming speed is switched to a half speed. M0 to M2 have a relationship of M0> M1> M2, which is obtained in advance from experiments or the like, and the data is stored in the ROM 143. It is not excluded that the administrator or the like of the printer 1 registers or changes values as necessary via input means such as an operation panel (not shown).

  As shown in FIG. 5, first, the toner amount in the buffer section 67 of the developing device 4 is detected (step S11). It is determined whether or not the detected toner amount M is larger than a reference value M0 (step S12). If it is determined that M> M0 (“YES” in step S12), if it is not currently half speed (“NO” in step S13), the process returns to the main routine as it is. In this case, assuming that a sufficient amount of toner is present in the buffer unit 67 (in the developing device 4), toner supply is not performed (time point a in FIG. 6).

On the other hand, if it is determined that M ≦ M0 (“NO” in step S12), if it is not currently half speed (“NO” in step S15), it is determined whether or not it is larger than M1 (step S15). S16).
If it is determined that M> M1 (M ≦ M0) (“YES” in step S16), toner replenishment 1 is performed (step S17), and the process returns to the main routine. The toner supply 1 is performed, for example, by operating the toner supply motor 55 (56) for a predetermined time t1 (several seconds or the like). Since the amount of toner in the buffer section 67 is decreasing (at the time point b in FIG. 6), toner is replenished in parallel with the current image forming operation.

For example, when image formation is performed on a document image having a low printing rate, the amount of toner in the buffer unit 67 increases in the direction of increase as shown by the broken line between bc in FIG. On the other hand, if toner supply cannot catch up when image formation is performed on a document image with a high printing rate, the amount of toner will shift in the direction of decreasing as shown by the solid line between bc.
When it is determined that M ≦ M1 is satisfied due to the reduction in the toner amount (“NO” in step S16), deceleration processing is executed (step S18) (time point c in FIG. 6).

FIG. 7 is a flowchart showing the contents of the deceleration processing subroutine.
As shown in the figure, toner replenishment 2 is performed (step S21). This toner replenishment 2 is basically performed in parallel with the current image forming operation similarly to the toner replenishment 1, but the replenishment time t2 is longer than t1. This is because M ≦ M1 and the amount of toner in the buffer section 67 is small, so that more toner is replenished with one toner replenishment.

  Then, after printing for the current Pth sheet is completed, the image forming speed is switched from the normal speed to half speed, printing for the (P + 1) th and subsequent sheets is executed (step S22), and the process returns. In this sense, when executing the processing of steps S16, S18, etc., the controller 14 cannot catch up with the toner supply by the toner supply control, and does not reach the specified amount (does not return) while the toner amount in the developing chamber is reduced. In this case, the image forming operation unit functions as an image forming control unit that performs control to make the image forming operation slower than a specified speed.

When the image forming speed is half speed, the amount of toner consumed per unit time is smaller than that at the normal speed, for example, half. Therefore, if the replenishment amount is larger than the toner consumption amount, the toner amount in the buffer unit 67 increases (between cd in FIG. 6).
When the image forming speed switching process is called again, the processes after step S11 are started in FIG. When the half speed control is being executed (between cd in FIG. 6), “YES” is determined in step S15 via steps S11 and S12, toner replenishment 2 is performed (step S19), and the process returns. . Toner replenishment 2 is the same as step S21.

During the half speed control, steps S11, S12, S15, and S19 are repeatedly executed until M> M0. If it is determined that M> M0 (“YES” in step S12), it is determined that the vehicle is in half speed (“YES” in step S13), and the return process is executed (step S14) (time point d in FIG. 6). .
FIG. 8 is a flowchart showing the contents of a subroutine for the return process.

As shown in the figure, when toner is being replenished, toner replenishment is stopped (step S31). After the image formation on the current Qth sheet is completed, the image forming speed is switched from the half speed to the normal speed, printing on the (Q + 1) th and subsequent sheets is executed (step S32), and the process returns. . As a result, the image forming speed returns to the original specified speed.
As described above, in this embodiment, when M ≦ M1 is detected, image formation on the subsequent sheets is executed at half speed, and toner is replenished in parallel during the half speed. When the half speed is selected, the job output is lower than that at the normal speed, but the rotation amount of the developing roller 61 during image formation for one sheet of the same size (how many times it has been rotated). Is the same at normal speed and half speed.

Therefore, if the remaining number is E at time c in FIG. 6, the rotation amount of the developing roller 61 after time c is an amount (Ga) corresponding to image formation on E sheets in this embodiment. ) Only.
On the other hand, in the case where toner is supplied by rotating the developing roller while interrupting printing as in the prior art, if the amount of rotation of the developing roller during the interruption period is Gb, only Ga is developed for E sheets after toner supply. Since the roller rotates, the total rotation amount becomes (Ga + Gb), and the rotation amount increases by Gb by toner replenishment. Since the developing roller 61, the supply roller 62, and the stirring roller 63 are driven to rotate at the same time, the rotation amount of the developing roller 61 is reduced, and the rotation amounts of the supply roller 62 and the stirring roller 63 are also reduced by the same amount. The stirring operation is also reduced.

  As described above, since the rotation amount of the developing roller 61 and the like can be reduced as compared with the conventional case, the toner in the developing chamber can be consumed by development before the deterioration of the toner due to stirring, and the deteriorated toner tends to remain in the developing chamber. In this way, stable image quality can be maintained and the life of a drive system such as a developing motor can be extended. In particular, as the developing roller 61 increases in its rotation amount, the thin resin layer provided on the surface wears due to friction with the supply roller 62, so that it is possible to reduce the rotation amount in the related art. Can extend the life. Further, it is not necessary to replace the toner replenishing motor with a high-speed one, and low cost can be realized.

  In the above configuration, printing is performed only on one side of the sheet. However, in the case of printing on both sides of the sheet, image formation is performed twice on one sheet (image formation on each of the first side and the second side). ) Is performed. Even in the case of both sides, switching the image forming speed in units of sheets is the same as in the case of only one side, but if the switching time is judged by the number of sheets, the first side and the second side cannot be distinguished, so the number of image formations It is desirable to judge by. In addition, the number of sheets may be used in place of the number of sheets even in a single-sided configuration. This is the same for the following embodiments.

<Second Embodiment>
In the first embodiment, the deceleration process is performed when M ≦ M1, but in the present embodiment, another condition is added as a condition for performing the deceleration process. The point is different from the first embodiment. Hereinafter, in order to avoid duplication of description, the description of the same contents as those of the above embodiment is omitted, and the same components are denoted by the same reference numerals.

FIG. 9 is a flowchart showing the contents of the image forming speed switching process according to the present embodiment, and shows only a different part from the flowchart of FIG. 5 in the above embodiment.
As shown in FIG. 9, when it is determined that the detected amount M ≦ M1 (“NO” in step S16), the image forming condition for the remaining number of sheets is 20 or more original images with a print rate of 50% or more. It is determined whether or not to print continuously (step S41). If it is determined that the condition is satisfied (“YES” in step S41), the process proceeds to deceleration processing (step S18). If it is determined that the condition is not satisfied (“NO” in step S41), the process proceeds to step S17. If image formation on the remaining number of sheets has a high printing rate and a large number of continuous sheets, there is a high probability that toner consumption will increase and toner replenishment will not be able to catch up. This is because it is unlikely that toner replenishment will not be able to catch up even if it does not shift to.

Thus, by determining whether or not it is necessary to shift to the half speed according to the expected toner consumption at the time of the next image formation, it is possible to further improve the productivity and the image quality.
Note that values such as the remaining number of sheets, the printing rate, and the number of continuous prints are acquired by referring to information written in the header of job data transmitted from the outside as execution conditions of the print job. . As for the printing rate, for each sheet, the ratio of the integrated area of the image portion to the area of the entire sheet is calculated, or the image portion actually formed with respect to the total number of dots when the image is formed on the entire surface of the sheet Or the ratio of the number of dots can be calculated.

Needless to say, the values of the printing rate and the number of continuous prints are not limited to those described above. Appropriate values can be set by experimentation in terms of productivity and image quality improvement. Alternatively, the process may be shifted to deceleration processing when either one of the printing rate and the number of continuous prints satisfies a predetermined condition.
<Third Embodiment>
In the above embodiment, the normal speed and the half speed are switched. However, in this embodiment, forcible toner supply for interrupting the image forming operation and supplying toner is executed only when a predetermined condition is satisfied. This point is different from the above embodiment.

  FIG. 10 is a flowchart showing the contents of the image forming speed switching process according to the present embodiment. As shown in the figure, in the case of half speed (“YES” in step S15), when the image forming operation time from the start of the half speed has not reached a predetermined time, for example, 60 seconds (in step S51). "NO"), go to step S19. In this case, the same processing as in the above embodiment is executed. The operating time is measured by a timer (not shown).

If the operation time has reached 60 seconds (“YES” in step S51), forced toner supply is executed (step S52), assuming that toner supply has not caught up even at half speed.
FIG. 11 is a flowchart showing the content of a subroutine for forced toner supply.
As shown in the figure, when the image formation for the P-th sheet currently being executed is completed, the image formation is interrupted (step S501). Here, a series of image forming operations from charging to transfer is interrupted. The image formation for the next (P + 1) th sheet is in a standby state.

Toner is supplied to the developing unit 4 that needs toner supply (step S502). For example, when Y toner is supplied, the color developing motor 52 and the toner supplying motor 55 are driven. Hereinafter, an example of Y color will be described.
The toner amount M in the buffer unit 67 of the developing unit 4 for Y color is detected (step S503), and it is determined whether or not the detected amount M> the reference value M0 (step S504).

If it is determined that M> M0 is not satisfied, that is, M ≦ M0 (“NO” in step S504), the process returns to step S502 to continue toner supply.
Steps S502 to S504 are repeatedly executed until M> M0. If it is determined that M> M0 (“YES” in step S504), assuming that the toner has been sufficiently supplied, the toner supply is stopped (step S505), and image formation on the (P + 1) th sheet is resumed at the normal speed. (Step S506), the process returns.

  As described above, when the half-speed operation time has reached a predetermined time, and when the condition is satisfied, the image formation is temporarily interrupted and the toner supply is performed. Since the half speed is continued in this state, it can be avoided that the toner amount falls below the value M2 and development is hindered. Note that the predetermined time (60 seconds in the above example) is obtained in advance from experiments and the like and stored in the ROM 143 as a value that is assumed that toner replenishment will not catch up even if the half speed is continued.

<Fourth embodiment>
In the third embodiment, the condition used as a criterion for executing the forced toner supply is that the half-speed operation time has reached a predetermined time. In the present embodiment, the toner in the current buffer unit 67 is used. The amount is M2 or less, and this point is different from the third embodiment.
FIG. 12 is a flowchart showing the contents of the image forming speed switching process according to the present embodiment. As shown in the figure, when the speed is half-speed (“YES” in step S15), the toner amount M in the buffer section 67 of the developing device 4 that is performing toner replenishment 2 is detected (step S61). It is determined whether or not the toner amount M is equal to or less than M2 (step S62).

If M> M2 (“NO” in step S62), the process proceeds to step S19. In this case, the same processing as in the first embodiment is performed. On the other hand, if M ≦ M2 (“YES” in step S62), the toner is forcibly supplied (step S52).
Since M2 is an amount that would impair development if the value falls below the value as described above, when the amount of toner in the buffer 67 becomes M2 or less, image formation is continued further. If not, it should be interrupted and toner replenishment started.

As described above, the determination as to whether or not the forced toner replenishment is necessary is made by directly detecting the toner amount in the buffer unit 67, so that the determination can be made more accurately.
In addition, the conditions for determining the execution of forced toner replenishment are not limited to those described above. For example, the number of continuous images formed at half speed may exceed a predetermined number. Whether or not the forced toner supply needs to be executed can be determined by managing the number of sheets. Also, two or more of the above conditions may be combined.

<Fifth embodiment>
In the present embodiment, the fixing temperature is also switched at the time of switching between the normal speed and the half speed, which is different from the above-described embodiment.
FIG. 13 is a flowchart showing the contents of the deceleration process according to the present embodiment.
As shown in the figure, after toner replenishment 2 is executed (step S21), after completion of image formation on the current Pth sheet, the temperature (fixing temperature) of the fixing roller 15 is switched from T0 to T1 (step S21). S71). Here, the temperature T1 is a temperature for half speed, and is a predetermined temperature, for example, 20 ° C. lower than T0. The reason why the fixing temperature is lowered at the half speed as compared with the normal speed is as follows. That is, since the conveyance speed of the sheet S is halved at the half speed, if the sheet is controlled at the same temperature at the normal speed and at the half speed, the sheet S is fixed when passing through the fixing unit 13 at the half speed. The amount of heat per unit time received from the unit 13 becomes too large, and depending on the type of sheet, curling or the like is likely to occur. Therefore, the temperature is lowered to some extent at half speed, and the amount of heat suitable for fixing at half speed is obtained. This is to supply to S.

  For example, the control unit 14 resets the target temperature of the fixing unit 13 from T0 to T1, and based on the current detection signal from the temperature detection sensor 17, the heater is set so that the fixing temperature is maintained at T1. This is done by controlling the energization of 18. Since the target temperature is T0 at the normal speed, the temperature of the fixing roller 15 is maintained at T0 higher than T1 at the time of switching. Therefore, switching the temperature of the fixing roller 15 from T0 to T1 actually stops the power supply to the heater 18 until the temperature of the fixing roller 15 decreases to T1.

When it is detected that the fixing temperature has decreased to T1, the image forming speed is switched from the normal speed to the half speed, image formation is performed on the (P + 1) th and subsequent sheets (step S72), and the process returns.
FIG. 14 is a flowchart showing the contents of the return processing according to this embodiment.
As shown in the figure, after the toner supply is stopped (step S21), after completion of image formation on the current Qth sheet, a process of returning the fixing temperature from T1 to T0 is executed (step S73). Specifically, for example, the target temperature of the fixing unit 13 is reset from T1 to T0, and the energization of the heater 18 is controlled based on the detection signal from the temperature detection sensor 17 so that the fixing temperature is maintained at T0. . Contrary to the deceleration process, in the return process, the fixing temperature is maintained at T1, so that power is supplied to the heater 18 to increase it to T0.

When it is detected that the fixing temperature has been raised to T0, the image forming speed is switched from the half speed to the normal speed, image formation is performed on the (Q + 1) th and subsequent sheets (step S74), and return is performed. To do.
As described above, since the fixing temperature is switched at the same time as switching between the normal speed and the half speed, there is an effect that power saving can be achieved while performing fixing more suitable for the image forming speed.

<Sixth Embodiment>
In the present embodiment, at the start of deceleration processing, it is selected whether to perform deceleration processing or forced toner supply according to the value of the remaining number of print jobs. This point is the first implementation. The form is different.
FIG. 15 is a flowchart showing the contents of the deceleration process according to the present embodiment.

As shown in the figure, when it is determined that the remaining number F is equal to or less than the predetermined value R (“YES” in step S81), the process proceeds to step S21, and the processing after S21, that is, the same processing as the deceleration processing shown in FIG. Execute. On the other hand, if it is determined that the predetermined value R is exceeded (“NO” in step S81), forced toner supply is executed (step S52).
The reason for selecting which process to execute in accordance with the value of the remaining number F is to end the print job earlier.

FIG. 16 is a diagram for explaining which of the cases where the toner can be forcibly replenished and the case where the deceleration process is executed, which of the remaining number of sheets can finish the job earlier.
As shown in the figure, in the case of forced toner replenishment, image formation is interrupted and toner replenishment is executed, and after completion of toner replenishment, the image forming operation for the remaining number of sheets is resumed at a normal speed. Therefore, if the time required for toner replenishment is U and the time required for image formation on one sheet S is H, the time W required to complete image formation for the remaining number of sheets F is expressed by U + (H × F). Can do.

On the other hand, in the case of deceleration (half speed control), the toner is replenished while the image forming speed is set to the half speed, so that W is (2H × F). Here, the image formation time for one sheet S at half speed is set to double that of the normal speed.
If the time W is distinguished from W1 for forced toner replenishment and W2 for deceleration processing, for example, U = 40 [seconds] and H = 2.5 [seconds], the remaining number of sheets F = 1 to 15 [sheets] ], W1> W2, when F = 16 [sheets], W1 = W2, and when F = 17 [sheets] or more, W1 <W2. Therefore, in this example, if the remaining number F is 1 to 15 [sheets], the deceleration process can finish the job earlier, and if it is 17 [sheets] or more, the forced toner supply can be completed earlier. become. If F = 16 [sheets], both are at the same time, but in the forced toner replenishment, the developing roller 61 is rotated during the image formation interruption period. It is desirable to select. Thus, in the above example, if the predetermined value R is set to 16, the job can be terminated earlier.

When the remaining number is large, the job processing speed (productivity) can be prioritized, which is convenient for a user who wants to improve productivity.
The configuration in which deceleration processing and forced toner supply are selected according to the remaining number of sheets can also be applied to the fifth embodiment in which the fixing temperature is switched from T0 to T1 during deceleration processing.
FIG. 17 is a diagram for explaining whether the forced toner supply or the deceleration process is executed according to the remaining number of sheets so that the job can be completed earlier in the configuration in which the fixing temperature is switched.

As shown in the figure, in the deceleration process, since the image forming operation for the remaining number of sheets is started at half speed after the temperature of the fixing roller 15 has decreased from T0 to T1, the time required for this temperature decrease is assumed. Is J, W2 is represented by J + (2H × F).
For example, if the time J is set to 20 [seconds] and the times U and H are set to the same values as described above, when the remaining number of sheets F = 1 to 7 [sheets], W1> W2 and F = 8 [sheets]. In this case, when W1 = W2 and F = 9 [sheets] or more, W1 <W2. Therefore, in this example, if the predetermined value R is set to 8, the job can be terminated earlier. The above times U, H, J and the like can be obtained from experiments and the like, and the predetermined value R can be set to an appropriate value for each apparatus from the obtained values.

<Modification>
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.
(1) In the above embodiment, the image forming speed is set to half speed in the deceleration process, but the present invention is not limited to this. For example, the speed may be set to 1/3 times or 3/4 times the normal speed. Further, the speed is switched in accordance with the image forming execution conditions for the remaining number of sheets (print rate, amount of remaining sheets, etc.), for example, 1/3 times for a high print rate and 3 / for a low print rate. It is also possible to switch to four times the speed. In the case of a high printing rate, it is assumed that a large amount of toner is consumed by development. Therefore, it is possible to prevent the toner supply from being caught up by dropping it as low as possible. On the other hand, since it is assumed that the toner consumption is small in the case of a low printing rate, the reduction in productivity can be suppressed by decelerating to a speed close to the normal speed.

Further, of the remaining number of sheets during deceleration, the speed from the first to the fifth sheet is 1/3 times the speed, the sixth to the 15th sheet is at a speed of 1/2 times, and the 16th and subsequent sheets are 2 / times. A configuration may be adopted in which the speed is switched for each sheet according to the image forming execution condition, such as a triple speed.
(2) In the above embodiment, an example in which the image forming apparatus of the present invention is applied to a tandem color digital printer has been described. However, the present invention is not limited to this. Regardless of color or monochrome image formation, any image forming apparatus provided with toner developing means can be applied to, for example, a copying machine, a FAX, an MFP (Multiple Function Peripheral), and the like.

The above embodiments and the above modifications may be combined.
(3) The present invention is not limited to an image forming apparatus, and may be an image forming method for switching an image forming speed. Furthermore, the method may be a program executed by a computer. The program according to the present invention includes, for example, a magnetic disk such as a magnetic tape and a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and a flash memory recording medium. It can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of the recording medium, wired and wireless various networks including the Internet in the form of programs, In some cases, the data is transmitted and supplied via broadcasting, telecommunication lines, satellite communications, or the like.

  Further, the program according to the present invention does not have to include all modules for causing the computer to execute the processing described above. For example, a separate information process such as a communication program or a program included in an operating system (OS) is performed. You may make it make a computer perform each process of this invention using the various general purpose programs which can be installed in an apparatus. Therefore, it is not always necessary to record all the modules on the recording medium of the present invention, and it is not always necessary to transmit all the modules. Further, there are cases where predetermined processing can be executed using dedicated hardware.

  The present invention can be widely applied to image forming apparatuses that require improvement in development performance and cost reduction.

1 is a diagram illustrating an overall configuration of a printer according to a first embodiment. FIG. FIG. 2 is a schematic diagram of a state in which a toner hopper provided in a printer and a developing device are connected as viewed from the direction of arrow A in FIG. 1. It is sectional drawing which shows the structure of a developing device. It is a block diagram which shows the structure of the control part with which a printer is equipped. It is a flowchart which shows the content of the image formation speed switching process. FIG. 6 is a diagram illustrating a transition of a toner amount due to switching of an image forming speed and toner supply. It is a flowchart which shows the content of the subroutine of a deceleration process. It is a flowchart which shows the content of the subroutine of a return process. It is a flowchart which shows the content of the image formation speed switching process which concerns on 2nd Embodiment. 10 is a flowchart illustrating the contents of an image forming speed switching process according to a third embodiment. 14 is a flowchart illustrating the content of a subroutine for forced toner supply according to a third embodiment. It is a flowchart which shows the content of the image formation speed switching process which concerns on 4th Embodiment. It is a flowchart which shows the content of the deceleration process which concerns on 5th Embodiment. It is a flowchart which shows the content of the return process which concerns on 5th Embodiment. It is a flowchart which shows the content of the deceleration process which concerns on 6th Embodiment. FIG. 10 is a diagram for explaining whether the forced toner supply or the deceleration process is executed according to the remaining number of sheets, so that the job can be completed earlier. In the configuration for switching the fixing temperature, it is a diagram for explaining which of the toner forcible replenishment and the deceleration process can be completed earlier depending on the remaining number of sheets.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 4 Developer 5 Transfer roller 10 Printer 13 Fixing part 14 Control part 21Y-21K Image forming part 25Y-25K Toner hopper 51 Main motor 52 Color development motor 53 Monochrome development motor 61 Development roller 65 Toner detection sensor 68 Toner 141 CPU
145 Image formation speed switching unit 146 Motor drive unit

Claims (8)

An image forming apparatus that visualizes a latent image formed on an image carrier with toner and then transfers the image onto a sheet to form an image,
A developing means for developing the latent image on the image carrier by conveying the toner in the developing chamber while stirring and carrying the toner on the developing roller during the image forming operation;
Toner replenishment control means for sequentially detecting the toner amount in the developing chamber, controlling toner replenishment according to the detection result, and adjusting the toner amount in the developing chamber to keep the specified amount;
An image forming control means for controlling the image forming operation to be slower than the specified speed when the toner supply by the toner supply control cannot catch up and the toner amount in the developing chamber does not reach the specified amount while decreasing;
An image forming apparatus comprising: The image formation control means includes
The image forming apparatus according to claim 1, wherein the image forming operation is returned to a specified speed when the toner amount in the developing chamber reaches a specified amount during the image forming operation controlled at a low speed. The image formation control means includes
When the printing rate at the time of image formation on the next sheet is equal to or higher than a predetermined value and / or when it is scheduled to continuously perform image formation on a plurality of sheets next, the control for delaying is performed. The image forming apparatus according to claim 1 or 2. A fixing means for thermally fixing the toner image transferred on the sheet to the sheet;
The image formation control means includes
4. The image forming apparatus according to claim 1, wherein, when performing the slowing-down control, the temperature of the fixing unit is made lower than the temperature at the specified speed. 5. A fixing means for thermally fixing the toner image transferred on the sheet to the sheet;
The image formation control means includes
When performing control to slow down, the temperature of the fixing unit is lowered from the temperature at the specified speed, and when image formation is performed by returning to the specified speed, the temperature of the fixing unit is set to the temperature at the specified speed. The image forming apparatus according to claim 2, wherein the image forming apparatus is returned. The image formation control means includes
(A) When the continuous operation time of image formation controlled at a slow speed reaches a predetermined time, (b) When the number of continuous executions of image formation controlled at a slow speed reaches a predetermined number, (c) Slow When at least one of (a) to (c) is satisfied when the toner amount in the developing chamber is reduced to an amount that is assumed to cause a problem in development during the speed-controlled image forming operation, the current image The image forming apparatus according to claim 1, wherein the toner supply is performed by temporarily interrupting the forming operation. The image formation control means includes
When an image forming job for continuously forming images on a plurality of sheets is being executed, the current image formation is interrupted and toner is replenished, and then the remaining sheets are supplied, rather than the control for slowing down. The forced toner supply is executed instead of the control for delaying the image forming job when the forced toner supply for restarting the image formation can be completed earlier. 2. The image forming apparatus according to item 1. The image formation control means includes
2. The image forming speed is changed for each sheet according to an image forming execution condition when performing image forming on a plurality of sheets continuously when performing the slowing control. 8. The image forming apparatus according to any one of 7 above.

Images