JP4590218B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system such as a copying machine or a printer.

  Conventionally, using an electrophotographic method or an electrostatic recording method, an image carrier is uniformly charged, and an electrostatic latent image is formed by changing the potential of the charged surface based on image information from external information. For example, an image forming apparatus for developing an electrostatic latent image using a developer, transferring the image to a recording medium, and performing an image forming process for fixing the image is shown in FIG. It has been.

  In this example, an electrophotographic image forming process is executed using the photosensitive drum 100 as an image carrier. The photosensitive drum 100 is formed by forming a photosensitive material layer (for example, an organic photosensitive material layer) on the surface of a cylindrical base made of aluminum, for example, and is driven to rotate. Around the photosensitive drum 100, in order from the upstream side in the rotation direction, a charging roller 101 as a charging unit, a laser beam scanning optical system (not shown) as an exposure unit as a latent image forming unit, and a developing unit as a developing unit. 102, a transfer roller 111 serving as a transfer unit, and a cleaner 109 serving as a cleaning unit are disposed.

  After the photosensitive drum 100 is uniformly charged by the charging roller 101, an electrostatic latent image is formed on the photosensitive drum 100 by laser beam scanning light. Then, a visible image is developed (developed) with toner (developer) in the developing device 102 in accordance with the electrostatic latent image.

  A recording medium, that is, transfer paper P, is fed in synchronism with the formation of a visible image (toner image) from a paper feed port (not shown), and a visible image is formed at a substantially abutting portion between the photosensitive drum 100 and the transfer roller 111. Upon receiving the transfer of the (toner image), the image on the transfer paper P is melted and fixed by the fixing device 110, and is discharged out of the apparatus as an image formed product.

  In an image forming apparatus that executes such an image forming operation, a developing device 102 as a developing unit includes a developing roller 103 as a developer carrying member, and a supply roller 105 that supplies nonmagnetic one-component toner (negative polarity) to the developing roller 103. In the vicinity of the supply roller 105, a stirring member 106 for conveying the toner in the container, a developing blade 104 as a developer regulating member for regulating the amount of toner on the developing roller 103, and the like are configured.

  Here, the developing roller 103 is formed of an elastic body in contact with the photosensitive drum 100. Further, the developing blade 104 is brought into light pressure contact with the developing roller 103 using the spring elasticity of a metal thin plate. A developing bias is applied to the developing roller 103 so that the toner is transferred from the developing roller 103 to the photosensitive drum 100 side by the developing bias power source 107 to have a predetermined potential.

  Here, as in the image forming apparatuses described in Patent Document 1 and Patent Document 2, a blade bias power source 108 is connected to the developing blade 104 as a developer regulating member in order to stabilize the toner charge amount. Then, a blade bias is applied so as to be a predetermined potential. There are various types of blade bias power supplies 108, such as those that supply the same potential as the development bias power supply 107, and those that supply different potentials.

  As described above, in the conventional image forming apparatus, by applying a fixed DC bias to each of the developing roller 103 and the developing blade 104, the toner is charged or the toner coating is stabilized.

  However, in such an image forming apparatus, it is difficult to stabilize the toner coat while preventing toner scattering, reversal toner adhering to the developing blade 104, and toner fusion to the developing blade 104.

  For example, when the image forming operation shown in the above conventional example was performed, the following problems were observed.

  As a first inconvenience, when the developing bias power supply 107 and the blade bias power supply 108 are set to the same potential in the above-described conventional example, there is a vertical streak-like density unevenness in a halftone image after image formation of about 1000 sheets. Occurred. This also appeared on the developing roller 103 that passed through the developing blade 104.

  As a result of observing the developing blade 104 at this time, a toner fusion lump was generated in the developing blade 104 in the vicinity of the contact portion between the developing blade 104 and the developing roller 103 and in the portion a on the fixed end side. Since the toner flow is blocked in the portion where the toner fused lump is present, the amount of toner on the developing roller 103 becomes thin, and vertical stripe-like density unevenness is generated on the image. This phenomenon of occurrence of vertical stripe-like density unevenness is included in the non-magnetic one-component toner used as a developer, as will be described below with reference to the schematic diagram showing the toner fusion state in FIG. This occurs because the external additives G 1 and G 2 to be fused to the developing blade 104.

  The nonmagnetic one-component toner T having negative polarity is composed of toner particles and external additives as auxiliary particles. The toner carried on the developing roller 103 has a negative polarity, and in a normal environment, the toner layer carried on the developing roller 103 that has passed through the developing blade 104 has a potential of about −20 to −50 V (Trek) (Measured with a surface potential meter model 334, manufactured by the company). At the contact portion c between the developing roller 103 and the developing blade 104, the surface of the developing blade 104 is always rubbed with toner, so that the external additive hardly adheres.

  However, since the portion a is downstream of the contact portion c between the developing roller 103 and the developing blade 104 in the rotation direction of the developing roller 103, the toner layer gradually moves away from the surface of the developing blade 103 in the portion a. A potential gradient will be generated. That is, even if the surface potentials of the developing roller 103 and the developing blade 104 are the same, the negatively charged toner layer carried on the developing roller 103 has a potential, so This is larger in negative polarity than the developing blade 104.

  Therefore, the negative external additive G1 adhering to the toner on the outermost surface of the toner layer separates from the toner surface and adheres to the surface a portion of the developing blade 104. The external additive G1 adhering to the surface a of the developing blade 104 gradually increases as the image formation proceeds, and the surface of the apparent developing blade 104 is roughened by the adhering external additive.

  For this reason, it is considered that the toner is trapped on the rough surface and is rubbed by the toner layer to be melted by frictional heat, thereby generating a toner fusion lump.

  Therefore, as shown in Patent Document 2, for example, when the developing roller 103 is supplied with a voltage of −300 V from the developing bias power source 107 and the developing blade 104 is supplied with −400 V from the blade bias power source 108, the developing roller 103 There is always a potential difference of about 100 V between 103 and the developing blade 104. As a result, it is possible to suppress the release of the negative external additive G1 from the toner layer surface from the toner surface even when the charge from the toner layer on the developing roller 103 is taken into account.

  However, when such a potential difference is provided, a second problem described below occurs.

  For example, when an image with a high printing rate that is almost similar to a solid image is output continuously, that is, in image formation in which a large amount of toner passes between the developing roller 103 and the developing blade 104, the density of the solid image A drop and vertical streaks occurred. This also appeared on the developing roller 103 that passed through the developing blade 104.

  Here, the printing rate refers to the ratio of the area where the toner is to adhere to the transfer paper P with respect to the printable area. Further, the printable area means an area obtained by removing the leading and trailing edges and the left and right margin areas (margins) from the entire area of the transfer paper P to be transferred. The area where the toner is to be deposited on the transfer paper P is determined by the area emitted by the exposure means. However, the region where the toner is to be deposited on the transfer paper P is the so-called reversal development in which the toner is supplied to the exposed portion of the photosensitive drum 100 to make the image visible, and the toner is supplied to the unexposed portion to be developed. This is different from so-called regular development in which an image is formed.

  In reversal development, the printing rate is 0% when the exposure means does not emit light, and the printing rate is 100% when the entire printable area is exposed. On the other hand, in normal development, the printing rate is 100% when there is no light emission from the exposure means, and the printing rate is 0% when the entire printable area is exposed.

  Hereinafter, the reverse development will be described in the present application.

  In the reversal development, the region where the toner is to be deposited on the transfer paper P as described above is controlled by the light emission of the exposure means. The light emission of this exposure means is determined by the image signal. Therefore, the printing rate is obtained by counting the number of pixels (number of pixels) of the light emission signal of the image signal.

  Here, as a result of observing the developing blade 104 to elucidate the cause of the occurrence of vertical stripes when an image with a high printing rate is output, the developing blade 104 is in the vicinity of the contact portion c between the developing blade 104 and the developing roller 103 and The toner adhered to the entire surface of the free end b section. The toner adhered was not melted, but was fixed to such an extent that it would not blow off even if air was blown with an air brush.

  Since the toner flow is blocked by the toner adhering to the portion b, the amount of toner on the developing roller 103 is reduced, and vertical stripe-like density unevenness is generated on the image.

  The case where the potentials of the developing roller 103 (−300 V) and the developing blade 104 (−400 V) are applied constantly will be specifically described.

  When the toner frictionally charged by the supply roller 105 reaches before the contact portion between the developing roller 103 and the developing blade 104 (near the portion b), the reversal toner (toner charged positively) mixed in the toner layer is obtained. It is attracted to the b portion on the surface of the developing blade 104 due to the influence of the potential difference. In particular, as the potential difference between the developing roller 103 and the developing blade 104 is increased, the reversal toner is attracted, so that the toner adhesion in the portion b of the developing blade 104 becomes worse.

  As toner adhesion increases, the amount of toner entering the vicinity of the portion b in front of the contact portion between the developing roller 103 and the developing blade 104 is blocked, so that the toner layer decreases. As a result, the density of the solid image has decreased. Furthermore, since the amount of toner adhered to the portion b of the developing blade 104 differs in the longitudinal direction, vertical streaks occur in addition to density reduction.

  Further, when solid images or images with a high printing rate are continuously output by several tens or more, toner fixation is generated earlier. This is because when an image having a high printing rate is continuously output, the toner tribo is lowered and the surface potential produced by the toner layer is lowered.

  Further, the problem occurred more remarkably particularly in the case of several hundred sheets from the start of printing by a new developing device. This is because the toner in the new developing device is in a state where the external additive is not firmly attached to the toner, and is easily released from the toner surface, and therefore easily follows the electric field between the developing roller 103 and the developing blade 104. It is.

  This phenomenon occurs particularly remarkably when the positive external additive G2 is mixed as the toner auxiliary particles in addition to the negative external additive G1. This phenomenon is considered to occur because the positive external additive first adheres to the free end of the developing blade 104, and the attached external additive traps the toner. The positive external additive G2 may be added in addition to the toner particles and the negative external additive in order to stabilize the chargeability and adjust the fluidity of the toner. Since the positive external additive G2 moves in the same manner as the reversal toner, it adheres to the portion b which is the free end of the developing blade 104. The fixed positive external additive G2 generates a decrease in density and vertical stripes as described above.

Further, the voltage applied to the developing blade 104 also requires fine control because the surface potential of the toner layer changes depending on the use environment. This is especially because the surface potential of the toner layer tends to be high in a low humidity environment and low in a high humidity environment.
Japanese Patent Laid-Open No. 03-125169 JP 05-011599 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing unit provided with a developer carrying member that can be rotated and a developer regulating member that regulates the amount of the developer carried on the developer carrying member. Prevents sticking and fusing of the developer to the surface, and prevents the toner from sticking even when images with a high printing rate are output continuously. An image forming apparatus capable of performing the above is provided.

The above object is manually achieved in the image forming equipment according to the present invention. In summary, the first aspect of the present invention is an image carrier in which an electrostatic latent image is formed on the surface based on image information;
A developing means for developing the electrostatic latent image with a developer, comprising a rotatable developer carrying member and a developer regulating member for regulating the amount of developer carried on the developer carrying member. When,
First voltage applying means for applying a voltage to the developer carrier;
Second voltage applying means for applying a voltage to the developer regulating member;
Control means for controlling operations of the first voltage applying means and the second voltage applying means;
Have
The developer includes toner particles, auxiliary particles having the same polarity as the charging polarity of the toner particles, and auxiliary particles having a polarity opposite to the charging polarity of the toner particles,
The developer regulating member is provided such that one end is a fixed end and the other end is a free end, and a contact portion with the developer carrying member exists in a region between the fixed end and the free end. And
In the control means, the potential relationship between the developer carrying member and the developer regulating member during the rotation of the developer carrying member is the same potential during image formation, and non-image formation after the image formation is performed. Controlling the first voltage application means or the second voltage application means so that the auxiliary particles of the same polarity at the time have the potential difference from the developer regulating member toward the developer carrier , The absolute value of the potential difference at the time of non-image formation is greater than the absolute value of the potential difference when the print rate calculated from the image information at the time of image formation is the first value. An image forming apparatus is provided , wherein the potential difference is controlled so that the absolute value of the potential difference at the second value larger than the second value becomes smaller .

According to a second aspect of the present invention, there is provided an image carrier on which an electrostatic latent image is formed on the surface based on image information;
A means for visualizing the electrostatic latent image with a developer, comprising: a rotatable developer carrying member; and a developer regulating member for regulating the amount of developer carried on the developer carrying member. Developing means, and a single voltage applying means for applying a voltage to both the developer carrier and the developer regulating member;
Delay control means for performing delay control of the voltage applied to the developer regulating member,
The developer includes toner particles, auxiliary particles having the same polarity as the charging polarity of the toner particles, and auxiliary particles having a polarity opposite to the charging polarity of the toner particles,
The developer regulating member is provided such that one end is a fixed end and the other end is a free end, and a contact portion with the developer carrying member exists in a region between the fixed end and the free end. And
In the delay control means, the potential relationship between the developer carrying member and the developer regulating member during rotation of the developer carrying member is the same potential during image formation, and a non-image after the image formation. At the time of formation, the voltage applied by the voltage applying means is changed, and the voltage fluctuation of the developer regulating member due to the change in the applied voltage is delayed and controlled between the developer carrying member and the developer regulating member. The auxiliary particles having the same polarity generate a potential difference from the developer regulating member toward the developer carrier , and the absolute value of the potential difference at the time of non-image formation is calculated from image information at the time of image formation. The potential difference is such that the absolute value of the potential difference when the printing rate is a second value larger than the first value is smaller than the absolute value of the potential difference when the calculated printing rate is a first value. It is characterized by controlling To provide an image forming apparatus.

  The image forming measure of the present invention can prevent the developer from adhering and fusing to the developer regulating member regardless of the image printing rate and the amount of developer carried by the developer carrying member. As a result, it is possible to prevent image defects such as a decrease in image density and vertical stripes, and to perform stable image formation over a long period of time.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
First, the image forming apparatus of this embodiment will be described with reference to FIG. The configuration and basic operation of each image forming unit installed in the image forming apparatus of the present embodiment are the same as those of the image forming apparatus shown in FIG. This is a reversal development system in which a toner as a developer is made visible and is visualized, and is a one-component image forming apparatus that performs development by bringing a developer carrier carrying negatively charged toner into contact with an image carrier.

  Therefore, also in this embodiment, the photosensitive drum 1 as an image carrier can be rotated in the direction of the arrow x. In the rotation process, the surface of the photosensitive drum 1 is uniformly charged to a negative polarity by a charging roller 2 as a primary charger. As the photosensitive drum 1 rotates, the uniformly charged surface is exposed by the exposure means 3. An electrostatic latent image is formed on the photosensitive drum 1 by the disappearance of the charge of the exposed portion.

  The developing device 4 is a developing unit that transfers toner as a developer to an exposed portion of the electrostatic latent image to visualize the electrostatic latent image. The toner used is a non-magnetic one-component toner. This embodiment is a so-called reversal development system that transfers toner to an exposed portion.

  The toner transferred onto the photosensitive drum 1 is transferred to the transfer paper P by a transfer roller 5 as a transfer charger. The toner remaining on the photosensitive drum 1 without being transferred is removed from the photosensitive drum 1 by the cleaning means 6.

  The toner on the transfer paper P is thermally melted by the fixing device 7 and melted and fixed on the transfer paper P to form a permanent image, which is discharged out of the apparatus as an image formed product.

  In the image forming apparatus of this embodiment, the developing device 4 includes a developing roller 8 as a developer carrying member, a supply roller 12 that supplies toner to the developing roller 8, a developing blade 9 as a developer regulating member, and a supply roller 12 The stirring member 13 is configured to convey toner to the side.

  The developing roller 8 can be rotated in the direction of arrow y, which is the forward direction of the photosensitive drum 1 by a motor 15 as a driving device. Since the developing roller 8 is so-called contact development in which development is performed in contact with the surface of the photosensitive drum 1, the developing roller 8 desirably has elasticity such as rubber. A voltage of about −300 V is supplied to the developing roller 8 from the developing bias power supply 10. The toner on the developing roller 8 is transferred to the exposed portion on the photosensitive drum 1 due to the difference between the exposed portion potential on the photosensitive drum 1 and the potential supplied from the developing bias power supply 10.

  On the other hand, the developing blade 9 is made of a thin metal plate and is brought into contact with the developing roller 8 by utilizing the spring elasticity of the thin plate. As the material of the metal thin plate, stainless steel, phosphor bronze, or the like can be used. In this example, a phosphor bronze thin plate having a thickness of 0.1 mm was used. By rubbing the developing blade 9 and the developing roller 8, the toner is triboelectrically charged and charged, and at the same time the layer thickness is regulated. A predetermined voltage is supplied to the developing blade 9 from a blade bias power supply 11.

  In this embodiment, a thin metal plate is used as the developing blade 9, but the present invention is not limited to this. For example, a conductive rubber or the like may be attached to the thin metal plate in a chip shape, or a conductive agent may be coated. .

  That is, in the image forming apparatus of this embodiment, the developing bias and the blade bias have power sources (developing bias power source 10 and blade bias power source 11) as first and second voltage applying units, respectively. By applying a DC bias, a configuration is adopted in which chargeability is imparted to the toner and uniform toner coating is promoted.

  The control device 14 serving as a control means includes a CPU and a ROM for controlling the rotation drive of the developing roller 8 and controlling the voltage values of the developing bias power supply 10 and the blade bias power supply 11 as voltage applying means. Yes.

  Further, in the image forming apparatus, a signal processing circuit 32 that performs signal processing of image information (image data) from the outside in a state connected to the control device 14, and the number of laser ON signals that are pixel signals indicating light emission are calculated. An arithmetic circuit 30 and a memory 31 for storing the addition result are installed. Here, the image information is information on individual dots constituting the electrostatic latent image formed on the photosensitive drum 1, and the arithmetic circuit 30 outputs the information for which a laser ON signal has been issued to this dot. Count. That is, the number of light emission is counted. The memory 31 stores the number of emitted lights during the previous image formation.

  Since the reversal development system is used, toner is consumed for pixels corresponding to the ON signal portion of the laser 3 in the image signal. Therefore, among the image signals processed into the bitmap data by the signal processing circuit 32, the ON signal of the laser 3 that consumes toner is added as image information and used at the time of the previous image formation. The number of dots made is counted.

  In this embodiment, the dot number V (pixel number: VK) of the laser ON signal is extracted from the bitmap data processed by the signal processing circuit 32. The extracted result is compared with a predetermined amount stored in the ROM of the control device 14 by the arithmetic circuit 30 and stored in the memory 31.

  As described above, by applying a DC bias from the respective power sources to the developing roller 8 and the developing blade 9 as a developing bias and a blade bias, respectively, a configuration that promotes charging of the toner and uniform toner coating. In the image forming apparatus in which the developing roller 8 is taken, as a feature of the present invention, the potential relationship between the developing roller 8 and the developing blade 9 during the rotation of the developing roller 8 is substantially the same during image formation, and is at least one during non-image formation. It is controlled to have a predetermined potential difference in the portion, and during the non-image formation, the external additive attached to the developing blade 9 is removed and the developing blade 9 is refreshed. Further, the bias for refreshing the developing blade 9 is controlled by the printing rate for image formation, thereby preventing toner sticking when images with a high printing rate are continuously output.

  In this embodiment, the printing rate is stored in the memory 31 by the number of laser ON signals, which are image signals obtained by processing the external information by the signal processing circuit 32 connected to the control device 14 by the method described above. However, the number of image signals (number of laser ON signals) in each dot with respect to the total number of dots constituting the electrostatic latent image formed on the photosensitive drum 1 stored in the memory 31. is there.

The present invention is also applicable in an image forming apparatus of regular development system, in that case, the toner adheres to the portion where the charge of the electrostatic latent image is not removed in the development step, the charge is as the image signal The dots corresponding to the portions that are not removed are counted. In addition to this, the image signal counting method is adapted to the latent image forming method so that signals corresponding to the amount of developer used are counted.

  As described above, since the toner is consumed for the pixels corresponding to the laser ON signal portion of the image signal, this printing rate corresponds to the amount of developer consumed for one image. In other words, an image with a high printing rate has a large amount of toner moving to the electrostatic latent image, and the influence of the toner fused and fixed to the developing blade 9 described in the conventional example appears over a wide area. Therefore, the effect is improved by controlling the bias for refreshing the developing blade 9 according to the printing rate.

  Here, in the present specification, when an image is formed, a visible image to be transferred to the image forming area (excluding the blank area) of the transfer paper P, which is a recording medium as an image formed product by the developing roller 8. It means the time during development.

  The non-image forming time means a time other than the image forming time and the time when the developing roller 8 is rotating, for example, the time corresponding to the blank area of the transfer paper P is used for the developing process. During this time, a visible image is not actually formed. For example, when rotating before preparation before image formation, after rotation after completion of image formation, or when forming images on transfer paper P and transfer paper P when printing multiple sheets. It means the time between paper (paper interval), the time of multiple rotations before preparation when the power is turned on.

  Here, the developing bias and blade bias applying method executed in the image forming step, which is a feature of the present invention in the above-described embodiment, will be described with reference to FIGS.

  FIG. 2 is a timing chart showing the operation sequence of each image forming means in the image forming operation according to the present embodiment. For example, the chart is shown as convex in the time when the photosensitive drum 1 and the developing roller 8 are rotationally driven. Further, regarding the operations of the developing bias power supply 10 and the blade bias power supply 11, the magnitude of the bias applied by them is represented by the height of the convex portion. Here, a case where two sheets are continuously printed is shown.

  FIG. 3 shows a flowchart according to these. This represents each control step in steps S1 to S11 in the order of execution. Here, an image forming operation when an image with a low printing rate is output on the first sheet and an image with a high printing rate is output on the second sheet will be described. In this embodiment, as described below, bias control is performed according to the image forming operation according to the flowchart shown in FIG. 3, and as a result, bias control of the developing bias and blade bias as shown in FIG. 2 is performed. The

  In this embodiment, since the photosensitive drum 1 and the developing roller 8 are always in contact with each other, the rotation of the photosensitive drum 1 and the rotation of the developing roller 8 are performed in synchronization. However, in the case of so-called non-contact development in which the photosensitive drum 1 and the developing roller 8 are always separated, or in the case of having a mechanism that can be separated even in contact development, the photosensitive drum 1 and the developing roller 8 The rotation may be performed asynchronously.

  According to the flowchart of FIG. 3, in step S1, a request for print output from a personal computer (not shown) is awaited. When there is a request for image formation, the potential difference between the developing blade 9 and the developing roller 8 at the previous image formation is read from the memory 31 in step S2. For example, assume that 500 V is selected as the potential difference.

  When the reading is completed, a pre-preparation rotation bias is applied as the rotation of the photosensitive drum 1 and the developing roller 8 starts in step S3. In the pre-preparation rotation, a voltage of about −300 V is applied from the developing bias power source 10. At the same time, a voltage of about −800 V is applied from the blade bias power supply 11 so as to correspond to the potential difference of 500 V (S3).

  In step S3, the beginning of the rotation of the developing roller 8 or the like is a preparatory rotation time before drawing an image, and is during non-image formation. During non-image formation, which is a time that does not affect the image on the transfer paper P, −800 V is applied to the developing blade 9 and −300 V is applied to the developing roller 8. That is, a potential difference that can be transferred from the developing blade 9 side to the developing roller 8 side is supplied to the negatively chargeable particles (toner and external additives). Therefore, immediately after the rotation of the developing roller 8 is started, the developing blade 9 is fixed from the contact portion c of the developing roller 8 (103 in FIG. 12) and the developing blade 9 (104 in FIG. 12) in FIG. In this embodiment, the negative external additive G1 adhering to the portion a which is the end side is transferred to the developing roller 8 side.

  In step S3, after applying -800V to the developing blade 9 and -300V to the developing roller 8 for a moment, the voltages of the developing bias power supply 10 and the blade bias power supply 11 become substantially the same potential of -300V. An image forming area is formed, image formation is performed, and image formation is started (S4).

  At the same time, the number of image signals (laser ON signals) in the electrostatic latent image formed on the photosensitive drum 1 when the first image is formed by the signal processing circuit 32 connected to the control means 14, that is, the exposure means 3. The number of luminescence is counted. Then, the required potential difference is returned to the control device 14 in comparison with a predetermined value stored in advance in the ROM in the control device 14 according to the number of pixels of the image calculated from here, that is, the printing rate (S5). Thus, the blade bias value to be applied at the next non-image formation is determined (S6).

  Here, in this embodiment, the comparison between the signal processing circuit 32 and the predetermined value stored in the ROM of the number of laser ON signals is the potential difference between the developing bias and the blade bias for the predetermined printing rate during non-image formation. The potential difference with respect to the current printing rate is obtained from the potential difference with respect to the predetermined value. Since the first printing is an image with a low printing rate, a large 500 V is set as the potential difference from the time of image formation. The potential difference value is stored in the memory 31 (S7).

  In this embodiment, the potential difference between the development bias and the blade bias is directly stored in the memory 31. However, the present invention is not limited to this, and the applied voltage of the development bias and the blade bias may be stored in the memory 31 as they are. Good.

  At the time of image formation, the surface potentials of the developing roller 8 and the developing blade 9 are substantially the same, so that the developing roller 8 rotates to move from the contact portion of the developing blade 9 to the fixed end side (a portion in FIG. 12). The negative external additive is transferred by the charge of the toner layer.

  Then, it is confirmed whether there is a next image formation request (S8).

  When the first image is formed, a so-called “paper gap” is formed between the next image formation. Between the sheets, a voltage of −800 V is applied to the developing blade 9 (S9). Due to the bias applied to the developing blade 9, the negative external additive attached to the fixed end side from the contact portion of the developing blade 9 during the first image formation is transferred to the developing roller 8 side.

  Since the transfer of the negative external additive on the fixed end side to the developing roller 8 is performed while the developing roller 8 is rotating, the negative external additive returns to the developing blade 9 side again. There is no.

  Further, since the toner carried on the developing roller 8 for outputting an image with a low printing rate is frictionally charged many times by the developing blade 9 and the supply roller 12, the external additive attached to the toner is strong with the toner. Adhering to Therefore, even if a large potential difference is applied between the developing blade 9 and the developing roller 8, the positive external additive does not adhere to the free end side of the developing blade 9.

  Then, the second image is formed similarly to the first image (S4). Even when the second image is formed, the biases of the developing bias power supply 10 and the blade bias power supply 11 are applied with substantially the same potential as in the first image (S4). Since the second image has a high printing rate, the developing roller 8 carries a toner with a charge that is not very high. For this reason, in the case of a high printing rate, the negative external additive does not deposit so much on the fixed end side of the developing blade 9.

  Here, during the second image formation, the number of laser ON signals with respect to the number of dots is counted as in the first image (S5, S6). However, since the second image is formed with a high printing rate, the potential difference between the developing blade 9 and the developing roller 8 is set low. As an example, since the printing on the second sheet is an image with a high printing rate, a small 70 V is set as the potential difference. The potential difference value is stored in the memory 31 (S7).

  Then, it is confirmed whether there is a next image formation request (S8).

  If there is no image formation request, the rotation after preparation for the next print is performed after the second image formation is completed (S10).

The developing blade 9 at this time, as shown in FIG. 1, the voltage of -370V to electrostatic position difference becomes 70V is applied. Since the image formation after preparation and before rotation (second sheet) has a high printing rate, toner with a charge not so high as tribo is carried on the developing roller 8 by the supply roller 12. For this reason, the toner from which the external additive is easily released approaches the upstream side of the contact portion between the developing blade 9 and the developing roller 8. However, since the potential difference between the developing blade 9 and the developing roller 8 is as low as 70 V, the electric field acting on the upstream side of the contact portion between the developing blade 9 and the developing roller 8 is small. For this reason, even if the toner easily releases the external additive, the positive external additive does not adhere to the free end of the developing blade 9. In the case of a high printing rate, a negative potential additive is not so much deposited on the fixed end side of the developing blade 9, so that a large potential difference is not required.

  Thereafter, when the rotation bias is turned ON, even when a high printing rate image is output by the bias applied to the developing blade 9, the positive external additive is fixed to the free end of the developing blade 9. Never do.

  In this embodiment, the printing rate is used in a binary manner depending on the magnitude of the printing rate. However, this is not limited to this, and an optimum potential difference may be applied after referring to the printing rate using a table of printing rate and potential difference. Good.

  Then, the rotation operation after the preparation is completed, and the rotation of the developing roller 8 and the photosensitive drum 1 is stopped (S11).

  In this way, the printing rate for image formation is counted, and when the printing rate is low, the negative external additive attached to the fixed end side from the contact portion of the developing blade 9 during image formation is developed during non-image formation. By setting a large potential difference between the blade 9 and the developing roller 8 and returning it to the developing roller 8 side, the developing blade 9 can be prevented from being fused and the developing blade 9 can be refreshed. When the printing rate is high, a positive external additive is deposited on the free end tip (part b in FIG. 12) of the developing blade 9 by reducing the potential difference between the developing blade 9 and the developing roller 8 during non-image formation. I will not let you.

  As a result, it is possible to prevent toner fusion and fixing to the developing blade 9 even if an image with a low printing rate or an image with a high printing rate is biased and continuously output.

  In this embodiment, a potential difference is provided between the developing bias power supply 10 and the blade bias power supply 11 during the pre-preparation rotation. However, the time for applying the potential difference is not limited to this, and a shorter time is also possible.

  Furthermore, it is possible to simultaneously control the application time at the same time as controlling the potential difference. That is, for an image with a high printing rate, the time for providing a potential difference is shortened, and for an image with a low printing rate, the time for providing a difference is increased.

  Further, when a refresh operation is performed by generating a potential difference between the developing roller 8 and the developing blade 9, the potential of the developing blade 9 is made larger than the potential of the developing roller 8 to the same polarity as the charging polarity of the developer. is required.

  In this embodiment, auxiliary particles were externally added to the toner particles (100 parts by weight). The externally added auxiliary particles added 1 part by weight of silica as a negative-polarity external additive and 0.1 part by weight of titanium oxide as a positive-polarity external additive. In particular, when a positive external additive is added, it is possible to adjust the fluidity of the toner and to impart stable chargeability to the toner. In the conventional example, since the positive external additive adheres to the free end tip b portion (FIG. 12) of the developing blade 104, it could not be used. In this embodiment, since the bias applied between the developing blade 9 and the developing roller 8 can be controlled, an image defect due to the positive external additive adhering to the free end of the developing blade 9 does not occur.

  These external additives are used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of toner particles. These external additives may be used alone or in combination. Those subjected to hydrophobic treatment are more preferable.

  When the added amount of the external additive is less than 0.01 part by weight, the fluidity of the one-component developer is deteriorated, and the transfer and development efficiency is lowered.

  On the other hand, when the amount of the external additive exceeds 10 parts by weight, excessive external additive adheres to the photosensitive drum 1 and the developing roller 8 to deteriorate the chargeability of the toner or disturb the image. .

  As described above, the potential difference acting on the developing roller 8 and the developing blade 9 is changed in accordance with the image information at least in part during non-image formation, so that the toner adhesion / deposition / deposition on the developing blade 9 is changed. It is possible to prevent fusion, and to prevent image density reduction and vertical stripes.

  That is, for example, by controlling the developing bias and the blade bias as shown in FIG. 2, that is, in the image forming apparatus of the present invention, the developing is performed while the developer carrying member that is the developing roller 8 is rotating. Since the potential relationship between the roller 8 and the developer regulating member that is the developing blade 9 is substantially the same during image formation and is controlled to have a predetermined potential difference at least during non-image formation, non-image formation is performed. At this time, the external additive attached to the developing blade 9 is removed, and the developing blade 9 is refreshed.

  By controlling the bias for refreshing the developing blade 9 according to the printing rate for image formation, it is possible to prevent the toner from sticking when an image with a high printing rate is continuously output.

  That is, for example, in this embodiment, the negative electrode attached to the fixed end side (a portion in FIG. 12) from the contact portion of the developing blade 9 with the developing roller 8 at substantially the same potential during image formation at every printing. When the external additive is transferred to the developing roller 8 side during non-image formation and the developing blade 9 is refreshed, the toner can be prevented from being fused to the developing blade 8, and the bias for refreshing the developing blade 9 is set as an image. Thus, even when the printing rate is particularly high, toner sticking on the free end side (b portion in FIG. 12) of the developing blade 9 from the contact portion with the developing roller 8 can be prevented. .

  Further, since this refresh operation is performed in a short time during non-image formation, even if reversal toner or a positive external additive adheres to the free end of the developing blade 9, development is performed by the potential of the toner layer during image formation. Since it acts so as to return to the roller 8, the external additive is not accumulated and deposited on the developing blade 8, and image defects such as vertical stripes and density reduction do not occur.

  In particular, in the present invention, when a potential difference is applied between the developing roller 8 and the developing blade 9 during non-image formation, it is important that the developing roller 8 is rotating. This is because even if the potential difference is applied in a state where the rotation of the developing roller 8 is stopped, it may reattach. The positive external additive returned to the developing roller 8 side by the rotation of the developing roller 8 is the fixed end side that is the downstream side in the rotation direction of the developing roller 8 at the contact portion between the developing blade 9 and the developing roller 8. It becomes possible to keep away from (a part in FIG. 12), and reattachment will be prevented.

  The potential difference applied to the developing roller 8 and the developing blade 9 during non-image formation is desirably 60V to 500V. This is because when the voltage is 60 V or less, the negative external additive attached to the developing blade 9 is difficult to transfer to the developing roller 8 side, and it is difficult to obtain the effect of preventing the fusion of the developing blade 9. The reason why the voltage is set to 500 V or less is that if it exceeds this level, the discharge between the developing roller 8 and the developing blade 9 tends to occur, and the current flowing between the developing blade 9 and the developing roller 8 increases, resulting in a high capacity. This is because a power source of 2 is required.

  In the present invention, a plurality of auxiliary particles can be used as auxiliary particles externally added to the toner. In particular, by using an external additive (positive polarity) having a polarity opposite to that of the toner as one of the auxiliary particles, the negative polarity external additive attached to the developing blade 9 is scraped off in combination with the rotation operation of the developing roller 8. It is also possible. Furthermore, excessive charge-up can be suppressed.

  In addition, it is preferable that at least the developing unit is configured as a cartridge that is detachable from the main body of the image forming apparatus. In this case, a developing cartridge in which only the developing unit is formed into a cartridge may be used. However, in addition to the developing unit, an image carrier, a charging unit, a cleaning unit, and the like are provided as in the image forming apparatus shown in FIG. 4 described in the second embodiment. More preferably, the process cartridge is integrated. As a result, the user's labor related to various maintenance operations such as toner replenishment and replacement of the developing device after the end of the service life can be reduced, and a stable output image can be obtained with a simple operation.

Example 2
In the image forming apparatus of the present invention, like the image forming apparatus having the configuration shown in FIG. 1 described in the first embodiment, the toner is charged between the developing roller 8 and the developing blade 9 in the developing process in the image forming process. The developing unit 4 is provided, and the potential relationship between the developing roller 8 and the developing blade 9 is set to substantially the same potential during image formation, and is controlled so as to have a predetermined potential difference at least at a part during non-image formation. It is characterized by that. As described above, in the image forming apparatus of the present invention, during non-image formation, a potential difference is generated between the developing roller 8 and the developing blade 9, and the external additive attached to the developing blade 9 is removed. By refreshing (refreshing operation), the occurrence of image thinness and vertical stripes is prevented.

  Further, in the present embodiment, as can be seen from the overall configuration of the image forming apparatus of the present embodiment shown in FIG. 4, the bias to the developing roller 8 and the developing blade 9 is applied by a single voltage applying unit 16. When the developing roller 8 and the developing blade 9 are set to substantially the same potential during image formation and the applied voltage is changed to change the potential of the developing roller 8 and the developing blade 9 during non-image formation, the developing blade is controlled by the delay control means 17. 9 is controlled (delay control) so as to delay the potential fluctuation of the developing roller 8 with respect to the potential fluctuation of the developing roller 8, thereby generating a potential difference between the developing roller 8 and the developing blade 9. In this embodiment, regarding the configuration of each image forming unit and the image forming operation, the same units and members as those shown in FIG. 1 are used except for the configuration of the power source for the developing bias and the blade bias.

  That is, in the power supply circuit, a relatively expensive transformer and a circuit system associated with the transformer can be replaced with an inexpensive delay circuit, so that the cost of the power supply circuit can be reduced.

  Further, by controlling the potential difference generated by the delay control means 17 based on the output image information, toner fusion to the developing blade 9 is possible even if an image with a low printing rate or an image with a high printing rate is biased and continuously output. And sticking can be prevented.

  As described above, in the image forming apparatus, since a potential difference can be generated between the developing roller 8 and the developing blade 9 by the single voltage application unit 16, the occurrence of image thinness and vertical stripes can be prevented with a simple configuration. it can.

  Therefore, since a separate power source is not required as compared with the first embodiment, the present invention can be implemented at low cost.

  Further, when the refresh operation is performed by generating a potential difference between the developing roller 8 and the developing blade 9, the potential of the developing blade 9 is more charged than the potential of the developing roller 8 as in the first embodiment. Increase to the same polarity side.

  That is, also in this embodiment, the negative external additive attached to the developing blade 9 is developed during non-image formation by setting the potential relationship between the developing roller 8 and the developing blade 9 to be substantially the same during image formation for each print. By transferring to the roller 8 side and refreshing the developing blade 9, sticking and fusing of the toner to the developing blade 9 are prevented.

  In this embodiment, the refresh operation is performed during non-image formation, that is, a time during which a portion corresponding to a blank area on the transfer paper P is used for development, during pre-preparation rotation before image formation, and after completion of image formation. For example, when -300 V is applied to the developing roller 8 when rotating after preparation, for example, between the sheets, a voltage higher than -300 V (for example, -360 V to -900 V) is applied to the developing blade 9 for a short time. To do. That is, it is a voltage that changes in an impulse manner, and is hereinafter referred to as “impulse voltage”. By applying this impulse voltage, a potential difference is generated between the developing blade 9 and the developing roller 8 thereafter. The potential difference acts so as to return the negative external additive attached at the time of image formation to the developing roller 8 side. At this time, the operation of changing in an impulse manner is an operation of applying a voltage for a short time of about 15 msec to 20 msec, which is larger in the same direction as the charging polarity of the developer than during image formation.

  The voltage may be applied for 20 msec or more. However, if this application time is too long, it is necessary to take a long interval between papers and the front rotation, etc., which leads to a decrease in throughput. . The application time may be set to 15 msec or less, but it is difficult to obtain a target voltage if it is made shorter than 15 msec due to a delay in the response of the power supply.

  By controlling the impulse voltage, the potential difference between the developing roller 8 and the developing blade 9 generated by the delay means connected to the developing blade 9 during non-image formation can be controlled.

  Therefore, also in this embodiment, by controlling the impulse voltage according to the image information, the potential difference generated between the developing blade 9 and the developing roller 8 is controlled, and the toner is fused and fixed to the developing blade 9. Can be prevented.

  The potential difference applied to the developing roller 8 and the developing blade 9 during non-image formation may be 60 V or more, desirably 60 V or more and 700 V or less, more preferably 60 V or more and 500 V or less. This is because if the voltage is 60 V or less, the negative external additive attached to the developing blade 9 cannot be transferred to the developing roller 8 side, and the effect of preventing fusion of the developing blade 9 cannot be obtained. is there.

  Further, since the effect is increased if the potential difference is large, the upper limit is not determined, but the allowable limit of leakage (dielectric breakdown) between the developing roller 8 and the developing blade 9 is a practical upper limit. However, since it is a single voltage application means and the accumulated charge is not large, it does not leak even if a potential difference of 700 V occurs. In addition, if the potential difference is 700 V, the object of the present invention can be sufficiently achieved. Further, the reason why the voltage is preferably 500 V or less is that when the voltage is 500 V or more, discharge is easily started between the developing roller 8 and the developing blade 9.

  Here, a specific image forming operation in this embodiment will be described with reference to FIGS.

  The image forming apparatus of this embodiment is a reversal developing system that visualizes by attaching toner to an exposed portion of a photosensitive drum 1 that is an image carrier, and a developing roller 8 carrying negatively charged toner is applied to the photosensitive drum 1. 1 is a one-component image forming apparatus for developing in contact.

  In the present embodiment, as shown in the overall configuration diagram of the image forming apparatus in FIG. 4, at least the photosensitive drum 1 and the developing means as the developing device 4 are integrated as the process cartridge H, and are attached to and detached from the image forming apparatus main body. It can be changed freely and can be replaced depending on the degree of wear. In this embodiment, the process cartridge H includes a charging roller 2 and a cleaning unit 6 in addition to the photosensitive drum 1 and the developing device 4.

  The control device (control means) 14 controls the rotational drive of the developing roller 8 and the voltage value supplied to the developing bias contact 19 and the blade bias contact 20. The impulse voltage is also controlled in response to the result from the arithmetic circuit 30 that processes the image information.

  In this embodiment, a high voltage power supply 16 as a single voltage applying unit is provided, and voltage is supplied to the developing roller 8 and the developing blade 9 via the developing bias contact 19 and the blade bias contact 20.

  In the high-voltage power supply 16, a delay control means 17 is arranged to perform delay control of a voltage branched from the developing bias contact 19 and supplied to the blade bias contact 20.

  The delay control means 17 is composed of a diode D1, a resistor R1, and a capacitor C1, and in this embodiment, R1: 100 MΩ and C1: 2200 pF.

  Control of the developing bias and blade bias by the control device 14 will be described with reference to FIGS. FIG. 5 is a timing chart showing the operation sequence of each image forming unit in the image forming operation according to the present embodiment shown in the same manner as FIG. Here, a case where two sheets are continuously printed is shown. FIG. 6 shows a flowchart according to these. Here, the control operation is shown in steps S21 to S33, and an image with a low printing rate (printing rate of about 1%) is formed in the previous image formation in a state close to a new developing device. A case where an image with a medium printing rate (printing rate of about 30%) is output as a second image with a high printing rate (printing rate of about 60%) will be described. In the present embodiment, as described below, bias control is performed according to the image forming operation according to the flowchart shown in FIG. 6, and as a result, bias control of the developing bias and blade bias as shown in FIG. 5 is performed. The

  Here, when applying the impulse voltage, it is desirable that the photosensitive drum 1 and the developing roller 8 be separated from each other. This is because if the impulse voltage is applied when the photosensitive drum 1 and the developing roller 8 are in contact with each other, the toner on the developing roller 8 may be developed on the photosensitive drum 1. If separation is not possible, the surface potential on the photosensitive drum 1 may be increased in advance.

  According to the flowchart shown in FIG. 6, a print output request is waited from a personal computer (not shown) in step S21. When there is a request for image formation, the process proceeds to step S22, and the previous impulse voltage value is read from the memory 31. It is assumed that, for example, −800 V is selected as the impulse voltage value because the previous image formation has a low printing rate.

  When the reading is completed, a development bias is applied to the contact 19 and the blade bias contact 20 with a pre-preparation rotation impulse voltage (−800 V) as the photosensitive drum 1 and the developing roller 8 start rotating in step S23.

  An impulse voltage of about −800 V is applied to the developing roller 8 and the developing blade 9, respectively, and at the same time, a voltage of about −800 V is applied to the blade bias contact 20. That is, the rise of the voltages supplied to the developing bias contact 19 and the blade bias contact 20 rises at almost the same timing.

  After about 20 msec, in step S24, the developing bias is lowered to a predetermined voltage (−300 V) by the impulse voltage applied during image formation. When the voltage supplied to the developing bias contact 19 and the blade bias contact 20 falls, the voltage supplied to the developing bias contact 19 falls immediately, but for the blade bias contact 20, as shown in FIG. The delay control means 17 falls with a time constant due to R1 and C1.

  As described above, the voltage applied to the developing roller 8 immediately falls and the voltage applied to the developing blade 9 gradually decreases, so that a potential difference is generated between the developing roller 8 and the developing blade 9. Therefore, a potential difference of 500 V at maximum occurs between the developing roller 8 and the developing blade 9. The potential difference of 500 V at maximum becomes smaller as time passes.

  This potential difference acts to transfer the negative external additive attached to the fixed end side from the contact portion of the developing blade 9 to the developing roller 8 side. As a result, the negative external additive adhering to the surface of the developing blade 9 is refreshed. Since this is performed while the developing roller 8 is rotating, the negative external additive does not return to the developing blade 9 side again.

  In step S25, the developing roller 8 is brought into contact with the photosensitive drum 1, and the developing bias contact 19 and the blade bias contact 20 are in the state of −300 V, which is substantially the same potential, and the photosensitive roller at the contact portion with the developing roller 8 is exposed. The surface of the drum 1 becomes the first image forming area, image formation is performed, and image formation is started. At the same time, the laser ON signal corresponding to the number of dots in the formed image, that is, the number of light emitted from the exposure means 3 is counted. Then, the required potential difference is returned to the control device 14 in comparison with a predetermined value stored in the ROM in the control device 14 in accordance with the calculated number of pixels of the image (S26). Thereby, the impulse voltage value to be applied at the time of the next non-image formation is determined (S27). As an example, since the first print is an image with a medium printing rate, 300 V is set as the potential difference. That is, −600 V is set as the impulse voltage.

  Then, the impulse voltage and the count value of the total number of output sheets are stored in the memory 31 (S28).

  During the image formation, since the developing roller 8 and the developing blade 9 have substantially the same potential, a negative polarity is caused by the charge of the toner layer from the contact portion of the developing blade 9 to the fixed end side by the rotation operation of the developing roller 8. The external additive is transferred. However, reversal toner, positive external additive and the like do not adhere to the developing blade 9.

  Then, it is confirmed whether or not there is a next image formation request (S29).

  When the first image is formed, a so-called “paper gap” is formed between the next image formation. Between the sheets, first, after the developing roller 8 is separated from the photosensitive drum 1, an impulse voltage (−600 V) is applied to the developing bias (S30). After approximately −600 V is applied to the developing roller 8 and the developing blade 9 for about 20 msec, the developing bias returns to a predetermined value (−300 V) in step S24.

  When the voltage supplied to the bias contact 19 and the blade bias contact 20 falls, the voltage supplied to the developing bias contact 19 falls immediately, but the blade bias contact 20 has a delay as shown in FIG. The control means 17 falls with a time constant due to R1 and C1.

  As described above, the voltage applied to the developing roller 8 immediately falls and the voltage applied to the developing blade 9 gradually decreases, so that a potential difference is generated between the developing roller 8 and the developing blade 9. Therefore, a potential difference of 300 V at maximum occurs between the developing roller 8 and the developing blade 9. The potential difference of 300 V at the maximum becomes smaller as time passes.

  Accordingly, the negative external additive attached to the fixed end side of the developing blade 9 by the previous image formation (medium printing rate) is returned to the developing roller 8 side. As a result, the negative external additive adhering to the surface of the developing blade 9 is refreshed. Since this is performed while the developing roller 8 is rotating, the negative external additive does not return to the developing blade 9 side again.

  In this embodiment, the speed of the voltage drop of the delay control means 17 is mainly determined by the electric charge accumulated in C1. However, as the developing roller 8 rotates and rubs against the developing blade 9 and the toner, negative charges are supplied from the developing blade 9. Therefore, the actual voltage drop by the delay control means 17 is shorter than the time constants of R1 and C1. In this embodiment, the potential difference between the developing roller 8 and the developing blade 9 was almost zero in a time of about 900 msec. In this embodiment, the interval between the sheets is 1 sec. During this interval, the potential difference based on the delay control is applied between the developing roller 8 and the developing blade 9 to sufficiently perform the refresh operation. .

  Therefore, after the refresh operation of the developing blade 9 is performed, the developing roller 8 is brought into contact with the photosensitive drum 1 again, and the second image is formed (S25). Here, similarly to the first sheet, during image formation, the negative external additive adheres and accumulates from the contact portion of the developing blade 9 to the tip of the free end as described above. At the same time, the number of dots at the time of image formation and the total number of output sheets are counted.

  Then, the required potential difference is returned to the control device 14 in comparison with a predetermined value stored in the ROM in the control device 14 in accordance with the calculated number of pixels of the image (S26). Thereby, the impulse voltage value to be applied at the time of the next non-image formation is determined (S27). As an example, since the printing on the second sheet is an image with a high printing rate, 70 V is set as the potential difference. That is, −370V is set as the impulse voltage. Then, the impulse voltage and the count value of the total number of output sheets are stored in the memory 31 (S28).

  Then, it is confirmed whether or not there is a next image formation request (S29).

  The developing roller 8 is separated from the photosensitive drum 1 when the image formation for the second sheet is completed and the rotation is performed after preparation for the next printing. Then, an impulse voltage (−370 V) is applied to the developing roller 8 and the developing blade 9 (S31). Similarly to the above, after −370 V is applied to the developing roller 8 and the developing blade 9 for about 20 msec, the developing bias returns to a predetermined value (−300 V) (S32).

  At this time, the delay control of the voltage applied to the developing blade 9 is performed in the same manner as between the sheets, and a voltage difference is generated between the developing roller 8 and the developing blade 9. However, since the impulse voltage is low, the capacity stored in the capacitor C1 of the delay control means 17 is small, the potential difference generated is small, and the application time is also short.

  For this reason, in the case of a high printing rate, a positive external additive or a reversal toner is applied to the free end side, instead of having a small effect of returning the negative external additive attached to the fixed end side of the developing blade 9 to the developing roller 8. The effect of transferring is reduced. Further, at a high printing rate, the action of depositing the negative external additive on the fixed end side of the developing blade 9 is small, so that it does not cause a problem by being fused to the developing blade 9.

  Then, the rotation operation after the preparation is completed, and the rotation of the developing roller 8 and the photosensitive drum 9 is stopped (S33).

  As described above, in this embodiment, the negative external additive attached to the fixed end side from the contact portion of the developing blade 9 at the time of image formation is applied between the developing blade 9 and the developing roller 8 at the time of non-image formation. The developing blade 9 can be refreshed by generating a potential difference (potential difference gradually decreasing by delay control) and returning the negative external additive to the developing roller 8. Then, by controlling the impulse voltage that changes the potential difference according to the image information, toner adhesion / deposition / fusion to the developing blade 9 can be prevented, and image density defects and vertical stripes can be prevented. It becomes possible.

  Note that the timing at which a predetermined potential difference is generated between the developing blade 9 and the developing roller 8 is during non-image formation. If a potential difference is generated between the two members during image formation, This is because the regulated toner carrying amount changes and a density step is generated on the image.

  In this embodiment, among the image forming elements, the developing means including toner, which is relatively consumed, is a cartridge that can be attached to and detached from the image forming apparatus main body H. Reduced labor. However, the configuration of the process cartridge as shown in FIG. 4 is not necessarily required, and only the developing device 4 may be a cartridge.

  Further, in this embodiment, the voltage delay control means 17 is provided in the high voltage power supply 16 of the image forming apparatus. However, the present invention is not limited to this. If the potential of the developing blade 8 can be controlled, the voltage is specifically controlled. As long as it is in the circuit for applying the voltage, it may be configured separately from the high-voltage power supply 16.

Example 3
In this embodiment, by controlling the potential difference generated by the delay control means according to the output image information, even if the image with a low printing rate or the image with a high printing rate is biased and continuously output, it is supplied to the developing blade. Preventing toner fusion and adhesion is the same as in the second embodiment.

  In this embodiment, by counting the number of images formed by the developing device 4 further, the potential difference can be more reliably controlled, and a good state can be maintained throughout the durability.

  FIG. 7 shows the overall configuration of the image forming apparatus of this embodiment. The image forming apparatus according to the present embodiment performs the same image forming operation as that of the first embodiment described with reference to FIG. 1 and includes a process cartridge H. FIG. The configuration is almost the same as that of the illustrated image forming apparatus. That is, it is a reversal development system in which toner is attached to the exposed portion of the photosensitive drum 1 that is an image carrier and visualized, and development is performed by bringing a developing roller 8 carrying negatively charged toner into contact with the image carrier. This is a component image forming apparatus.

In the present embodiment, the number counting section 33 is provided, counts the number of image formation i.e. the total number of output sheets of the developing device 4. The counting result is reflected in the calculation of the impulse voltage value.

Figure 8 is a diagram for explaining control by the total number of output sheets of the developing device 4 in this embodiment by the number counting means 33, it is shown the relationship between the printing ratio and the impulse voltage at the plurality of total number of output sheets as a graph Yes. As shown here, the impulse voltage value is determined by the image printing rate as in the second embodiment, and the impulse voltage is set lower when the printing rate becomes higher. That is, the potential difference during non-image formation is set high when the printing rate is low, and is set low when the printing rate is high.

  As shown here, when the total number of output sheets is large (curve f in FIG. 8) compared to when the total number of output sheets is small (curve e in FIG. 8), the impulse voltage with respect to the printing rate is high. That is, the impulse voltage with respect to the printing rate is set to increase as the total number of output sheets increases.

  The reason for this setting is that the liberation of external additives from the toner decreases as the number of output sheets increases, and conversely, the degree of toner fusion to the blade 9 due to toner deterioration increases.

Here according to the control device 14, the control of the developing bias and blade bias corresponding to the number counting section 33, FIG. 9 will be described with reference to FIG. 10. FIG. 9 is a timing chart showing the operation sequence of each image forming unit in the image forming operation according to the present embodiment shown in the same manner as in FIGS. Here, a case where two sheets are continuously printed is shown. FIG. 10 shows a flowchart according to these. Here, the control operation is shown in steps S51 to S63, and an image with a low printing rate (printing rate of about 1%) is formed in the previous image formation in a state close to a new developing device. A case where a high printing rate image (printing rate of about 60%) is output to the second sheet as a printing rate image (printing rate of about 30%) will be described. Also in this embodiment, as described below, bias control is performed from the standby state according to the image forming operation in steps (steps) S51 to S63 according to the flowchart shown in FIG. The bias control of the developing bias and the blade bias is performed. Further, in the present embodiment, a sequence at the time of 2000 sheets will be described as compared with the second embodiment.

  In FIG. 10, a print output request is waited from a personal computer (not shown) (S51). When there is a request for image formation, the previous impulse voltage value is read from the memory 31 (S52). It is assumed that, for example, −800 V is selected as the impulse voltage value because the previous image formation has a low printing rate.

  When the reading is completed, with the start of rotation of the photosensitive drum 1 and the developing roller 8, a pre-preparation rotation impulse voltage (−800V) is applied to the contact 19 and the blade bias contact 20 (S53). An impulse voltage of about −800 V is applied to the developing roller 8 and the developing blade 9, respectively, and at the same time, a voltage of about −800 V is applied to the blade bias contact 20. That is, the rise of the voltages supplied to the developing bias contact 19 and the blade bias contact 20 rises at almost the same timing.

  After the applied impulse voltage is about 20 msec, the developing bias is lowered to a predetermined voltage (-300 V) applied to the developing roller during image formation (S54). When the voltage supplied to the developing bias contact 19 and the blade bias contact 20 falls, the voltage supplied to the developing bias contact 19 falls immediately, but for the blade bias contact 20, R1 and C1 of the delay control means 17 Will fall with a time constant.

  As described above, the voltage applied to the developing roller 8 immediately falls and the voltage applied to the developing blade 9 gradually decreases, so that a potential difference is generated between the developing roller 8 and the developing blade 9. Therefore, a potential difference of 500 V at maximum occurs between the developing roller 8 and the developing blade 9. The potential difference of 500 V at maximum becomes smaller as time passes.

  Then, the developing roller 8 is brought into contact with the photosensitive drum 1.

  When the voltages of the developing bias contact 19 and the blade bias contact 20 are approximately the same potential of −300 V, the first image forming area is formed (image formation).

  At the same time, the number of dots and the total number of output sheets at the time of image formation are counted (S55). Then, the required potential difference is returned to the control device 14 in comparison with a predetermined value stored in the ROM in the control device 14 according to the calculated number of pixels of the image and the current total number of output sheets (S56). Thereby, the impulse voltage value applied at the time of the next non-image formation is determined (S57).

  Here, the impulse voltage value during the next non-image formation is as shown in the blade bias chart e of FIG. 9 when the developing device 4 is close to the initial state as shown by the curve e of the graph of FIG. In addition, an impulse voltage of 300 V is applied as in the second embodiment. However, when the number of output sheets is as large as 2000 as shown by the curve f in the graph of FIG. 8, 500 V is set as the potential difference as shown in the blade bias chart f of FIG. That is, −800V is set as the impulse voltage.

  Then, the impulse voltage and the count value of the total number of output sheets are stored in the memory 31 (S58).

  During the image formation, since the developing roller 8 and the developing blade 9 have substantially the same potential, a negative polarity is caused by the charge of the toner layer from the contact portion of the developing blade 9 to the fixed end side by the rotation operation of the developing roller 8. The external additive is transferred. However, reversal toner, positive external additive and the like do not adhere to the developing blade.

  Then, it is confirmed whether there is a next image formation request (S59).

  When the first image is formed, a so-called “paper gap” is formed between the next image formation. Between the sheets, first, after the developing roller 8 is separated from the photosensitive drum 1, an impulse voltage (−800V) is applied to the developing bias (S60). For about 20 msec, −800 V is applied to the developing roller 8 and the developing blade 9, and then the developing bias returns to a predetermined value (−300 V) (S54).

  When the voltage supplied to the bias contact 19 and the blade bias contact 20 falls, the voltage supplied to the developing bias contact 19 falls immediately, but the blade bias contact 20 is caused by R1 and C1 of the delay control means 17. It falls with a time constant.

  As described above, the voltage applied to the developing roller 8 immediately falls and the voltage applied to the developing blade 9 gradually decreases, so that a potential difference is generated between the developing roller 8 and the developing blade 9. Therefore, a potential difference of 500 V at maximum occurs between the developing roller 8 and the developing blade 9. The potential difference of 500 V at maximum becomes smaller as time passes. Accordingly, the negative external additive attached to the fixed end side of the developing blade 9 by the previous image formation (medium printing rate) is returned to the developing roller 8 side. As a result, the negative external additive adhering to the surface of the developing blade 9 is refreshed. Since this is performed while the developing roller 8 is rotating, the negative external additive does not return to the developing blade 9 side again.

  That is, when the developing device 4 is close to the initial state, the impulse voltage is suppressed at the medium printing rate, and the potential difference between the developing roller 8 and the developing blade 9 is reduced, so that the external additive that is likely to be in the initial state is easily obtained. Prevents blade sticking due to loosening. When the total number of output sheets increases, the impulse voltage can be increased so as to prevent blade fusion to prevent blade fusion.

  Then, the developing roller 8 is brought into contact with the photosensitive drum 1 and the second image is formed. At the time of image formation, the negative external additive adheres and accumulates from the contact portion of the developing blade 9 to the fixed end as described above. However, since the printing on the second sheet is an image with a high printing rate, the amount of adhesion is very small. At the same time, the number of dots and the total number of output sheets at the time of image formation are counted (S55). Then, the required potential difference is returned to the control device 14 in comparison with a predetermined value stored in the ROM in the control device 14 according to the calculated number of pixels of the image and the current total number of output sheets (S56). Thereby, the impulse voltage value applied at the time of the next non-image formation is determined (S57). As an example, the second print is an image with a high printing rate, so 300 V is set as the potential difference. That is, −600 V is set as the impulse voltage. Then, the impulse voltage and the count value of the total number of output sheets are stored in the memory 31 (S58).

  Also here, when the developing device 4 is close to the initial state, the impulse voltage is suppressed at a high printing rate, and the potential difference between the developing roller 8 and the developing blade 9 is reduced, so that an external additive that is easily placed in the initial state can be obtained. Prevent blade sticking due to loosening. When the total number of output sheets increases, the impulse voltage can be increased so as to prevent blade fusion to prevent blade fusion.

  Then, it is confirmed whether there is a next image formation request (S59).

  The developing roller 8 is separated from the photosensitive drum 1 when the image formation for the second sheet is completed and the rotation is performed after preparation for the next printing. Then, an impulse voltage (−600 V) is applied to the developing roller 8 and the developing blade 9 (S61). Similar to the above, after −600 V is applied to the developing roller 8 and the developing blade 9 for about 20 msec, the developing bias returns to a predetermined value (−300 V) (S62).

  Then, the rotation operation after the preparation is completed, and the rotation of the developing roller and the photosensitive drum is stopped (S63).

  As described above, in this embodiment, the negative external additive attached to the fixed end side from the contact portion of the developing blade 9 at the time of image formation is applied between the developing blade 9 and the developing roller 8 at the time of non-image formation. The developing blade 9 can be refreshed by generating a potential difference (potential difference gradually decreasing by delay control) and returning the negative external additive to the developing roller 8. Then, by controlling the impulse voltage from which the potential difference is varied according to the image information and the total number of output sheets, toner adhesion / deposition / fusion to the developing blade 9 can be prevented regardless of the number of output sheets. Defects and vertical stripes can be prevented.

  In this embodiment, the potential difference between the developing roller 8 and the developing blade 9 is controlled by the impulse voltage. However, since the time constant of the CR circuit is used, the capacitance (C) and resistance (R) of the capacitor are used as controls. It is also possible to control with variable.

  In this embodiment, the number of images formed by the developing device 4 is added to the condition for controlling the potential difference between the developing bias and the blade bias at the time of non-image formation, but other conditions such as environmental conditions may be added. it can.

  Further, in this specification, the description has been made using a single color developing device, but this is not particular. Of course, the present invention can also be applied to a color image forming apparatus using a plurality of developing devices.

  Furthermore, although the contact developing method is used as the developing device, the present invention can also be applied to a non-contact developing method using an elastic developing roller.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. 6 is a timing chart illustrating an example of an image forming operation according to the present invention. 3 is a flowchart illustrating an example of an image forming operation according to the present invention. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on this invention. 6 is a timing chart showing another example of the image forming operation according to the present invention. 6 is a flowchart illustrating another example of the image forming operation according to the present invention. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on this invention. It is a graph which shows the relationship between the applied voltage value by a single voltage means by the number of image formation sheets based on this invention, and a printing rate. 6 is a timing chart showing another example of the image forming operation according to the present invention. 6 is a flowchart illustrating another example of the image forming operation according to the present invention. It is a schematic block diagram which shows an example of the conventional image forming apparatus. FIG. 6 is a diagram illustrating a phenomenon in which toner external additives are fixed and fused on a developer regulating member.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Developer (Developer)
8 Development roller (developer carrier)
9 Development blade (developer regulating member)
10 Development bias power supply (first voltage applying means)
11 Blade bias power supply (second voltage applying means)
14 Control device (control means)
16 High voltage power supply (single voltage application means)
17 the delay control unit 31 memory 32 signal processing circuit 33 number counting means H process cartridge (cartridge)

Claims (6)

An image carrier on which an electrostatic latent image is formed on the surface based on image information;
A developing means for developing the electrostatic latent image with a developer, comprising a rotatable developer carrying member and a developer regulating member for regulating the amount of developer carried on the developer carrying member. When,
First voltage applying means for applying a voltage to the developer carrier;
Second voltage applying means for applying a voltage to the developer regulating member;
Control means for controlling operations of the first voltage applying means and the second voltage applying means;
Have
The developer includes toner particles, auxiliary particles having the same polarity as the charging polarity of the toner particles, and auxiliary particles having a polarity opposite to the charging polarity of the toner particles,
The developer regulating member is provided such that one end is a fixed end and the other end is a free end, and a contact portion with the developer carrying member exists in a region between the fixed end and the free end. And
In the control means, the potential relationship between the developer carrying member and the developer regulating member during the rotation of the developer carrying member is the same potential during image formation, and non-image formation after the image formation is performed. Controlling the first voltage application means or the second voltage application means so that the auxiliary particles of the same polarity at the time have the potential difference from the developer regulating member toward the developer carrier , The absolute value of the potential difference at the time of non-image formation is greater than the absolute value of the potential difference when the print rate calculated from the image information at the time of image formation is the first value. An image forming apparatus , wherein the potential difference is controlled so that the absolute value of the potential difference when the second value is larger than the second value is smaller . An image carrier on which an electrostatic latent image is formed on the surface based on image information;
A means for visualizing the electrostatic latent image with a developer, comprising: a rotatable developer carrying member; and a developer regulating member for regulating the amount of developer carried on the developer carrying member. Developing means, and a single voltage applying means for applying a voltage to both the developer carrier and the developer regulating member;
Delay control means for performing delay control of the voltage applied to the developer regulating member,
The developer includes toner particles, auxiliary particles having the same polarity as the charging polarity of the toner particles, and auxiliary particles having a polarity opposite to the charging polarity of the toner particles,
The developer regulating member is provided such that one end is a fixed end and the other end is a free end, and a contact portion with the developer carrying member exists in a region between the fixed end and the free end. And
In the delay control means, the potential relationship between the developer carrying member and the developer regulating member during rotation of the developer carrying member is the same potential during image formation, and a non-image after the image formation. At the time of formation, the voltage applied by the voltage applying means is changed, and the voltage fluctuation of the developer regulating member due to the change in the applied voltage is delayed and controlled between the developer carrying member and the developer regulating member. The auxiliary particles having the same polarity generate a potential difference from the developer regulating member toward the developer carrier , and the absolute value of the potential difference at the time of non-image formation is calculated from image information at the time of image formation. The potential difference is such that the absolute value of the potential difference when the printing rate is a second value larger than the first value is smaller than the absolute value of the potential difference when the calculated printing rate is a first value. It is characterized by controlling Image forming apparatus.   In the non-image formation in which the delay carrying means is rotating and the image forming by the developing means is not performed, the applied voltage by the voltage applying means is compared with that in the image forming. 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is changed in an impulse manner so as to increase toward the same polarity as the charging polarity.   The image forming apparatus according to claim 1, wherein the potential difference is 60V to 500V.   4. The image forming apparatus according to claim 1, wherein the potential difference is controlled in accordance with the number of images formed using the developing unit. The non-image forming time is a time other than the image forming time and the developer carrying member is rotating. During the image forming time, the developing means is transferred onto the recording medium as an image formed product. the image forming apparatus according to any one of claims 1-5, characterized in that the time in which to develop the electrostatic latent image corresponding to the image.

Images