Image forming apparatus

Abstract

To provide an image forming apparatus that employs a contact development system and is not provided with a contact and separation mechanism, and can effectively prevent transfer of developer from a developer carrier to an image carrier during a preliminary rotation operation.SOLUTION: When the difference between voltage applied from first voltage application means to a developer carrier and voltage applied from second voltage application means to a supply member when an image forming operation is performed is a first supply contrast, and the difference between voltage applied from the first voltage application means to the developer carrier and voltage applied from the second voltage application means to the supply member when a preliminary rotation operation is performed is a second supply contrast, control means performs control so that the second supply contrast becomes smaller than the first supply contrast or have a polarity opposite to that of the first supply contrast.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an image forming apparatus. In particular, it relates to an electrophotographic image forming apparatus that uses an electrophotographic recording method.

Background Art

[0002] Conventionally, in an image forming apparatus such as an electrophotographic printer, an image forming apparatus using a "contact development method" in which development is performed with a photosensitive drum and a developing roller in contact is widely known.

[0003] In an image forming apparatus using the "contact development method", there is a configuration in which a "pre-rotation operation" is performed before the "image forming operation" is started, or a "post-rotation operation" is performed after the "image forming operation" is completed. In the "pre-rotation operation" or "post-rotation operation", a rotating member such as a developing roller or a photosensitive drum may be controlled to rotate.

[0004] Specifically, the "pre-rotation operation" is performed from the start of rotation of the rotating member until the "image forming operation" is started. On the other hand, the "post-rotation operation" is performed after the "image forming operation" is completed until the rotation operation of the rotating member is completed (stopped).

[0005] During the "pre-rotation operation" or "post-rotation operation", a configuration in which the developing roller and the photosensitive drum are separated is known. However, if an "abutment and separation mechanism" for abutting and separating the photosensitive drum and the developing roller is provided in the image forming apparatus, the image forming apparatus tends to become complicated and large-sized.

[0006] On the other hand, in order to simplify and miniaturize the image forming apparatus, an image forming apparatus without an "abutment and separation mechanism" has been proposed (Patent Document 1).

[0007] In Patent Document 1, since the developing roller and the photosensitive drum are in a "constant" contact state, control is performed to suppress the transfer of toner from the developing roller to the photosensitive drum during periods other than the image forming operation. Specifically, in Patent Document 1, after the image forming operation is completed, the potential of the photosensitive drum is set to "0 V" and a "positive polarity" voltage is applied to the developing roller, so that toner having a "negative polarity" charge on the developing roller is held on the developing roller without being transferred to the photosensitive drum.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, if the time (stop period) is long from the end of the previous image forming operation to the next image forming operation, the charge of the toner may decay over time.

[0010] In this case, since the toner on the developing roller has lost its charge (negative polarity), even if a "positive polarity" voltage is applied to the developing roller, the "electrical holding force" for holding the toner that has lost its charge on the developing roller does not work, and the toner may be transferred onto the photosensitive drum. Such a phenomenon in which toner is transferred from the developing roller to the photosensitive drum regardless of the image forming operation is also called "development fogging".

[0011] When the "development fogging" phenomenon occurs, not only is extra toner consumed, but in some cases, the transferred toner is further transferred from the photosensitive drum to the transfer roller. Then, the back surface of the conveyed paper comes into contact with the transfer roller to which the toner is attached ru As a result, toner is further transferred to the back surface of the paper, which may cause the paper to become dirty.

[0012] Therefore, in view of the above problems, the present invention provides an image forming apparatus that employs a contact development method and does not provide a contact separation mechanism, and can effectively suppress the transfer of developer from the developer carrier to the image carrier during the previous rotation operation.

Means for Solving the Problems

[0013] The image forming apparatus of the present invention includes: an image carrier that carries an electrostatic latent image on its surface; a charging member that charges the surface of the image carrier, a developer carrier that contacts the surface of the image carrier and performs an image forming operation for developing the electrostatic latent image to form an image; charged to a normal polarity a supply member that contacts the surface of the developer carrier and supplies developer to the developer carrier; a developing voltage applying means for applying a developing voltage to the developer carrier; charging voltage application means for applying a charging voltage to the charging member, control means for controlling the developing voltage applying means; the charging voltage application means, The control means is configured to: and, control the image forming operation and a first rotation operation executed before the image forming operation to be executable; in the first rotation operation, when starting the first rotational operation, the surface of the image carrier is in contact with the surface of the developer carrier, rotate the surface of the image carrier and the surface of the developer carrier in contact with each other; a charging voltage less than the discharge start voltage is applied to the charging member, and when performing the image forming operation, set a potential difference formed between the developer carrier and the supply member as a first potential difference; when performing the first rotation operation, set a potential difference formed between the developer carrier and the supply member as a second potential difference; when performing the first rotation operation, set a potential difference formed between the developer carrier and the supply member as a second potential difference; the control means is configured to: in the first rotational operation, control such that the second potential difference is smaller than the first potential difference. ru yo This is the gist of the present invention.

[0014] Another image forming apparatus of the present invention includes: an image carrier that carries an electrostatic latent image on its surface; A developer carrier that carries on its surface a developer charged to a normal polarity for performing an image forming operation of developing the electrostatic latent image by contacting the surface of the image carrier and forming an image. A supply member that contacts the surface of the developer carrier and supplies the developer to the developer carrier. Developing voltage applying means for applying a developing voltage to the developer carrier. Control means for controlling the developing voltage applying means, and having: The control means is controllably configured to execute the image forming operation and a second rotation operation executed after the image forming operation. In the second rotation operation, the surfaces of the image carrier and the developer carrier are rotated in contact with each other to execute a stop operation. When performing the image forming operation, a potential difference formed between the developer carrier and the supply member is defined as a first potential difference. When performing the second rotation operation, when a potential difference formed between the developer carrier and the supply member is defined as a third potential difference, The control means performs control such that in the second rotation operation, with the developing voltage having a reverse polarity, which is opposite to the normal polarity, applied to the developer, the third potential difference becomes smaller than the first potential difference. agent carrier This is the gist of the invention.

Advantages of the Invention

[0015] According to the present invention, in an image forming apparatus that employs a contact development method and does not provide a contact / separation mechanism, during the previous rotation operation, the transfer of the developer from the developer carrier to the image carrier can be effectively suppressed.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the materials, shapes, relative arrangements, etc. of the components described in the embodiments should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions, and the scope of the present invention is not intended to be limited to the following embodiments.

[0018] (Embodiment 1) <Configuration of the image forming apparatus> FIG. 1 is a cross-sectional conceptual diagram of an image forming apparatus according to Embodiment 1 of the present invention.

[0019] As shown in FIG. 1, the image forming apparatus M of the present embodiment is an electrophotographic monochrome laser printer. The photosensitive drum 1 (image carrier) is rotatably supported by the apparatus main body M1 and is rotationally driven in the R1 direction at a process speed (peripheral speed) of 150 mm / S by a drive source (not shown).

[0020] Around the photosensitive drum 1, in order along its rotation direction, a charging roller 2 (charging member), an exposure device 3 (exposure means), a developing device 4 (developing means), and a transfer roller 5 (transfer means) are arranged. The transfer roller 5 sandwiches the paper P with the photosensitive drum 1 and transfers the toner image from the photosensitive drum 1 onto the paper P by applying a transfer voltage from a transfer power source (not shown).

[0021] Further, a cassette 7 storing the paper P is arranged at the lower part of the apparatus main body M1, and a paper feed roller 8, a conveyance roller 9, a fixing device 12, a discharge roller 15, and a discharge tray 16 are arranged in order along the conveyance path of the paper P from the cassette 7.

[0022] In addition, a control unit C (control means) is provided in the apparatus main body M1 of the image forming apparatus, and controls the rotation operations of the rollers and the control of the voltage application means.

[0023] <Configuration of Developing Device> FIG. 2 is , this a cross-sectional conceptual diagram of a developing device 4 of an image forming apparatus according to an embodiment of the invention.

[0024] As shown in FIG. 2, the developing device 4 is provided with a developing roller 42 (developer carrier), a supply roller 43 (supply member), and a developing blade 44 (restricting member). Note that the supply roller 43 is arranged to contact the developing roller 42 and can supply toner to the developing roller 42 or scrape toner from the developing roller 42. Further, a stirring rod 45 (stirring member) for stirring the toner is provided substantially at the center of the toner container 4a.

[0025] Developing roller 4 to 2 is connected to a developing voltage power source 50 (first voltage application means). Further, a supply voltage power source 51 (second voltage application means) is connected to the supply roller 43.

[0026] Next, the operation of the developing device 4 in this embodiment will be described.

[0027] As shown in FIG. 2, in the developing device 4, when the stirring rod 45 rotates in the R2 direction, toner is temporarily stored in the vicinity region T of the contact portion between the developing roller 42 and the supply roller 43. Then, the stored toner is supplied to the developing roller 42 by the supply roller 43 rotating in the R3 direction. Further, the toner supplied to the developing roller 42 passes through the developing blade 44 (restricting member) as the developing roller 42 rotates in the R4 direction and is thinned (coated) to a predetermined layer thickness.

[0028] Note that in this embodiment, the toner (developer) supplied to the developing roller 42 is triboelectrically charged to the normal polarity "negative polarity" by rubbing against the developing blade 44.

[0029] Then, the toner (layer) coated on the developing roller 42 is conveyed to a developing nip formed by the opposing of the developing roller 42 and the photosensitive drum 1 as the developing roller 42 rotates in the R4 direction.

[0030] At the developing nip, an electric field is formed by the electrostatic latent image potential formed on the photosensitive drum 1 by the exposure device 3 and the developing voltage V3 applied from the developing voltage power supply 50 to the developing roller. Also, due to this electric field, a part of the toner coated on the developing roller 42 is transferred to the region of the electrostatic latent image on the photosensitive drum 1. As a result, the "electrostatic latent image" is developed (visualized) as a "toner image (developer image)".

[0031] At the developing nip, the toner remaining on the developing roller 42 without being used for development is scraped off by the supply roller 43 rotating at the contact portion between the developing roller 42 and the supply roller 43, and at the same time, the toner stored in the region T is newly supplied onto the developing roller 42.

[0032] In addition, in this embodiment, after the toner image is transferred from the photosensitive drum 1, the toner remaining on the surface of the photosensitive drum 1 is transferred from the photosensitive drum to the developing roller by the electric field formed by the photosensitive drum (surface potential V2) and the developing voltage V3 applied to the developing roller. That is, the toner remaining on the surface of the photosensitive drum 1 is transferred to the developing roller and finally scraped off and recovered by the supply roller 43. Therefore, in this embodiment, there is no need to provide a dedicated cleaning means for cleaning the surface of the photosensitive drum 1.

[0033] <Output Setting of Voltage> Hereinafter, the output settings of the voltages (V1 to V4) for the "image forming operation S2" during image formation, the "post-rotation operation S3" at the end of image formation, and the "pre-rotation operation S1" at the start of image formation in this embodiment will be described.

[0034] Note that FIG. 3 is a sequence chart from the "pre-rotation operation" to the "post-rotation operation" in the image forming apparatus according to Embodiment 1.

[0035] Note that the "previous rotation operation" means the rotation operation of rotating the photosensitive drum, developing roller, etc. until receiving the image information to be printed and until the "image forming operation" starts (i.e., until the transition to the potential for image formation is completed).

[0036] On the other hand, the "subsequent rotation operation" means the rotation operation in which, after the "image forming operation" ends (i.e., after the transition from the potential for image formation starts), the photosensitive drum, developing roller, etc. continue to rotate for a while without stopping.

[0037] (1) "Image forming operation S2" during image formation First, the output setting of the voltage during the "image forming operation S2" will be described.

[0038] As shown in FIG. 3, in this embodiment, during the image forming operation S2, the drum potential V2 of the photosensitive drum (the surface potential after charging by the charging roller 2) is set to "-500V", which is a potential suitable for image formation. Specifically, a charging voltage V1 of "-1000V" is applied from a charging power source (not shown) to the charging roller 2 to charge the surface of the photosensitive drum 1 (resulting in the drum potential V2).

[0039] On the other hand, a developing voltage V3 of "-350V" is applied to the developing roller 42 from the developing voltage power source 50. Therefore, Vback (=V3 - V2), which is the difference between the developing voltage V3 and the drum potential V2 (-500V) of the photosensitive drum, is "150V".

[0040] Note that if the potential difference Vback is too small, toner having a charge of a normal polarity (e.g., negative polarity) may transfer to the photosensitive drum even during non-image formation.

[0041] Conversely, if the potential difference Vback is too large, during image formation, toner having a charge of an abnormal polarity (e.g., positive polarity) may transfer to the photosensitive drum at locations not related to the image.

[0042] In this embodiment, the developing voltage V3 during the image forming operation is set to "-350 V" so that the potential difference Vback becomes an appropriate value.

[0043] On the other hand, the supply voltage V4 applied to the supply roller 43 is set to output a voltage based on the amount of toner coated on the developing roller 42.

[0044] In this embodiment, "-550 V" is applied as the supply voltage V4. Therefore, during the image forming operation (S2), the supply contrast (first supply contrast) ΔV1S2 (= V3 - V4) which is the voltage difference is "200 V" by subtracting the supply voltage V4 "-550 V" from the developing voltage V3 "-350 V". During the image forming operation (S2), due to the first supply contrast, toner is supplied from the supply roller 43 to the developing roller 42 by the action of an electric force.

[0045] As will be described later, generally, if the supply contrast (V3 - V4) is too large, the amount of toner coating on the developing roller increases, so the rubbing opportunity between the surface of the developing blade 44 and each toner particle decreases, and there is a possibility that sufficient charge cannot be imparted to the toner. In this case, the force for electrically holding the toner on the developing roller 42 tends to be insufficient, and the possibility of the toner peeling off from the developing roller 42 becomes high.

[0046] Conversely, if the supply contrast (V3 - V4) is too small, the amount of toner supplied to the surface of the developing roller 42 decreases, so the image density of the formed image may become low. Further, when the supply contrast is a "negative value" (that is, when the magnitude relationship between V3 and V4 is reversed and the "voltage difference" becomes "reverse polarity"), an "electric force" in the direction of moving the toner acts from the developing roller 42 side to the supply roller 43 side. For this reason, the toner is scraped off from the developing roller 42 by the supply roller 43, and the possibility of the image density becoming lower becomes even higher.

[0047] In this way, by adjusting the supply contrast (V3 - V4), the supply amount of toner from the supply roller to the developing roller can be controlled. Furthermore, by suppressing the amount of toner supplied to the developing roller, the "rubbing (charging) opportunity" for the toner can be improved, and the charge amount (polarity) of the toner can also be adjusted.

[0048] (2) "Post-rotation operation S3" at the end of image formation Next, the output setting of the voltage during the "post-rotation operation S3" after the image formation operation S2 is completed will be described.

[0049] In this embodiment, as shown in FIG. 3, after the image formation operation S2 is completed, the drum potential V2 of the photosensitive drum 1 is set to "0V" to by controlling the charging voltage V1.

[0050] As a result, during the "pre-rotation operation S1" when the next image formation is performed, regardless of the attenuation of the drum potential V2 of the photosensitive drum 1, the drum potential V2 always becomes the state of "0V". That is, if the potential V2 of the photosensitive drum is controlled (set) to "0V" during the post-rotation operation S3, the drum potential V2 can always start from "0V" during the next image formation.

[0051] Therefore, when starting the next image formation (during the pre-rotation operation S1), if a voltage of a predetermined polarity (for example, positive polarity) is applied to the developing roller with respect to the drum potential "0V", toner of the opposite polarity (for example, negative polarity) to the predetermined polarity can be electrically held on the developing roller. That is, during the control at the pre-rotation operation S1 during the next image formation, it is not necessary to consider the "degree of attenuation of the drum potential" according to the elapsed time from the previous image formation.

[0052] In this embodiment, immediately after the "image formation operation S2" is completed, the drum potential V2 is "-500V". Therefore, in this embodiment, during the post-rotation operation S3, control (S3a) is performed to lower (change) the charging voltage V1 step by step from "-1000V" to "-500V" in increments of "100V" so that the drum potential V2 becomes "0V".

[0053] As a result, the drum potential V2 also rises stepwise every "100 V" in the same manner, and finally the drum potential becomes "0 V".

[0054] On the other hand, in this embodiment, during the post-rotation operation S3, the developing voltage V3 is synchronized with the lowering control (S3a) of the charging voltage V1 so as to maintain the "150 V" which is Vback during the image forming operation S2. Specifically, for the developing voltage V3 and the supply voltage V4, control is performed to lower (change) them stepwise every "50 V" (S3b, S3c).

[0055] By performing such control, even during the post-rotation operation S3, the toner on the developing roller 42 can be electrically held without being transferred to the photosensitive drum, similar to the image forming operation S2.

[0056] Note that, in this embodiment, during the post-rotation operation S3, the developing voltage V3 is "150 V" and the supply voltage V4 is "-50 V". Therefore, the supply contrast (the third supply contrast) ΔV3S3 (= V3 - V4) during the post-rotation operation S3 becomes "200 V", which is the same as the (first) supply contrast during the image forming operation.

[0057] Also, as shown in FIG. 3, in this embodiment, the normal charging polarity of the developer is "negative polarity", and during the post-rotation operation S3, control S3a (lowering control) is performed to gradually change the drum potential V2 from "-500 V" to "0 V". On the other hand, if the normal charging polarity of the developer is "positive polarity", during the post-rotation operation S3, control (lowering control) may be performed to gradually change the drum potential V2, for example, from "500 V" to "0 V". The same applies to the developing voltage V3 and the supply voltage V4.

[0058] (3) "Pre-rotation operation S1" at the start of image formation Next, the output setting of the voltage during the "pre-rotation operation S1" before the start of the image forming operation S2 will be described.

[0059] As described above, by setting the drum potential V2 to "0V" during the "post-rotation operation S3" after the previous image formation, the drum potential V2 also becomes "0V" at the start of the "pre-rotation operation S1" in the next image formation.

[0060] In this embodiment, as shown in FIG. 3, during the pre-rotation operation S1, a developing voltage V3 of "+150V" is applied to the developing roller 42. On the other hand, the drum potential V2 is "0V". Therefore, Vback (= V3 - V2) becomes "150V", which is the same value as during the image formation operation S2.

[0061] Thus, in this embodiment, during the "pre-rotation operation S1", it is possible to suppress the transfer of toner on the developing roller 42 to the photosensitive drum 1, similar to during the image formation operation S2 and the post-rotation operation S3.

[0062] Note that when the elapsed time since the end of the previous image formation operation is long, it is conceivable that the charge of the toner on the developing roller 42 decays over time.

[0063] When the charge of the toner decays, the action of the "electrical force" for holding it on the developing roller 42 weakens. Therefore, when the developing roller 42 and the photosensitive drum 1 rotate in contact, there is a possibility that the toner will transfer from the developing roller 42 to the photosensitive drum 1.

[0064] Note that the charge of the toner on the developing roller 42 increases (increases) according to the number of passes (and rubbing) through the developing blade 44 as the developing roller 42 rotates. However, when the cumulative number of rotations of the developing roller 42 is small, there is a possibility that the charge of the toner will not reach a sufficient charge to be held on the developing roller 42.

[0065] That is, as long as the developing roller and the photosensitive drum are in contact, there is a possibility that the toner on the developing roller 42 will continue to transfer to the photosensitive drum 1 until the toner has sufficient charge.

[0066] Therefore, in this embodiment, in order to apply charge to the toner with attenuated charge at an early stage, in the previous rotation operation S1, by setting the output voltage differently from that during the image forming operation S2, the transfer of the toner onto the photosensitive drum can be reduced.

[0067] Specifically, during the "previous rotation operation S1" before the image forming operation S2, the supply voltage V4 applied to the supply roller 43 is set to "150V". Thereby, the supply contrast (second supply contrast) ΔV2S1 (=V3 - V4) can be set to "0V".

[0068] That is, the "(first) supply contrast" ΔV1S2 during the image forming operation S2 is "200V". Compared with the image forming operation S2, during the previous rotation operation S1, the (second) supply contrast ΔV2S1 is smaller. As a result, the amount of toner supplied from the supply roller 43 to the developing roller 42 is less, and the amount of toner coated on the developing roller 42 is also less.

[0069] As a result, the toner has more opportunities to rub against the developing blade 44 and can have charge at an early stage due to frictional electrification.

[0070] In this way, during the previous rotation operation S1, by adjusting the supply voltage and reducing the (second) supply contrast, the amount of toner supplied to the developing roller 42 can be suppressed. And since the rubbing opportunity between the toner on the developing roller 42 "per grain" and the developing blade 44 increases, during the previous rotation operation S1, the charge of the toner becomes high at an early stage, and the "development fog (amount)" can be suppressed. That is, during the previous rotation operation S1, the transfer of the toner from the developing roller to the photosensitive drum is suppressed.

[0071] Note that in this embodiment, after rotating the photosensitive drum 1 at a predetermined rotation speed with the drum potential V2 of "0V", in order to set (switch) the drum potential V2 during the image forming operation S2 to ("-500V"), control (S1a) is performed to raise (change) the charging voltage V1.

[0072] Specifically, as shown in FIG. 3, immediately before the image forming operation S2 starts, control S1a is performed to raise the charging voltage V1 stepwise at intervals of "100V", and the drum potential V2 of the photosensitive drum 1 is set to "-500V" by the time the image forming operation S2 starts.

[0073] That is, when the charging voltage is increased stepwise from "-500V" to "-1000V", the drum potential V2 also rises stepwise at intervals of "100V", and finally the drum potential becomes "-500V".

[0074] Also, similar to the "post-rotation operation S3", during the pre-rotation operation S1 as well, the developing voltage V3 is synchronized with the raising control (S1a) of the charging voltage V1 so that Vback during the image forming operation S2 maintains "150V". Specifically, for the developing voltage V3 and the supply voltage V4, control is performed to raise them stepwise (change) at intervals of "50V" (S1b, S1c).

[0075] As shown in FIG. 3, in this embodiment, the normal charging polarity of the developer is "negative polarity", and during the pre-rotation operation S1, control S1a (raising control) is performed to change the drum potential V2 stepwise from "0V" to "-500V". On the other hand, when the normal charging polarity of the developer is "positive polarity", during the pre-rotation operation S1, control (raising control) may be performed to change the drum potential V2 stepwise from "0V" to, for example, "500V". The same applies to the developing voltage V3 and the supply voltage V4.

[0076] <Comparative Example 1> Next, the effects of the present invention will be described by using a comparison with Comparative Example 1.

[0077] To confirm the effects of the present invention, the amount of "development fog" (development fog amount) during the "pre-rotation operation" in Example 1 was measured.

[0078] Also, as a comparison with Example 1, the same measurement was performed on Comparative Example 1.

[0079] Figure 4 is a sequence chart from the "forward rotation operation" to the "reverse rotation operation" of Comparative Example 1.

[0080] Table 1 shows the output settings of each voltage during the forward rotation operation S1 in Example 1 and Comparative Example 1.

[0081]

Table 1

[0082] As can be understood from Table 1 or Figure 4, in Comparative Example 1, the value of the (second) supply contrast ΔV2S1 of the forward rotation operation S1 is set to be different from that of Example 1.

[0083] Specifically, as shown in Table 1 or Figure 4, in Comparative Example 1, the supply voltage V4 is set to "-50V" so that the (second) supply contrast becomes "200V" during the forward rotation operation S1. On the other hand, in Example 1 (refer to Table 1 or Figure 3), the supply voltage V4 and the developing voltage V3 are also set to "150V" so that the (second) supply contrast becomes "0" during the forward rotation operation S1.

[0084] The comparative experiments related to Comparative Example 1 and Example 1 were conducted in a "high temperature and high humidity" environment where the toner charge is likely to decay. Specifically, it was conducted in an environment with a temperature of 30°C and a relative humidity of 80%.

[0085] The interval between image formations was adjusted so that the elapsed time since the previous image formation ended was "3 hours". In order to quantify (measure) the "developing fog amount", "taping" was performed on the surface of the photoreceptor drum where developing fog occurred, and the concentration of the toner adhering to the tape after taping (the amount of toner adhesion per unit area of the adhesive surface of the tape) was measured with a densitometer.

[0086] As the densitometer used in the comparative experiment, DENSITOMETER TC-6DS / A (TOKYO DENSHOKU Co., LTD) was used. The measurement (taping) locations were the surfaces of the photoreceptor drum 1 facing the circumferential surface of the developing roller 42 at the 1st, 5th, and 10th rotations of the developing roller 42, starting from the start of the previous rotation operation S1.

[0087] Table 2 shows the measurement (comparison) results of the development fog density (%) for Example 1 and Comparative Example 1.

[0088]

Table 2

[0089] As shown in Table 2, at the 1st rotation of the developing roller, there was no significant difference in the development fog density between Example 1 and Comparative Example 1. However, at the 5th and 10th rotations, it was confirmed that the "development fog density" of Example 1 was significantly lower than that of Comparative Example 1.

[0090] This is because the supply contrast of Comparative Example 1 ([[]] second ) is "200V", while in Example 1, the supply contrast ([[]] second ) is small ("0V"). Therefore, compared with Comparative Example 1, in Example 1, less toner is supplied from the supply roller 43 to the developing roller 42, and the rubbing opportunity between the toner and the surface of the developing blade per grain of toner increases when passing through the developing blade 44. Thus, it is presumed that the charge of the toner increased earlier in Example 1.

[0091] In this way, by adjusting the output setting of the voltage, even in a configuration where the developing roller 42 and the photoreceptor drum are always in contact, it is possible to suppress the transfer of toner to the photoreceptor drum (the "development fog" phenomenon) during the "previous rotation operation" before the start of the image forming operation.

[0092] (Example 2) Next, Example 2 of the present invention will be described with reference to FIG. 5. The configuration of the image forming apparatus in Example 2 is basically the same as that in Example 1. Hereinafter, the main differences will be described.

[0093] FIG. 5 is a sequence chart from the "previous rotation operation" to the "subsequent rotation operation" in the image forming apparatus according to Example 2 of the present invention.

[0094] Note that Example 2 is different from Example 1 in that the output setting of the voltage during the "subsequent rotation operation S3" after the image forming operation is completed is different.

[0095] On the other hand, the output setting of the voltage during the "previous rotation operation S1" before the image forming operation starts is the same as that in Example 1.

[0096] Table 3 shows the output setting of the voltage during the "subsequent rotation operation S3" in Example 2. For reference, the output setting of the voltage in Example 1 is also shown together.

[0097]

Table 3

[0098] As shown in Table 3, in Example 1, during the subsequent rotation operation S3, the supply voltage V4 was "-50V", and the (third) supply contrast ΔV3S3 was "200V" as in the image forming operation S2. On the other hand, in Example 2 compared to Example 1, during the subsequent rotation operation S3, the supply voltage V4 was set to "150V", and the (third) supply contrast ΔV3S3 was set to " 0V ".

[0099] That is, Example 2 is different from the configuration of Example 1 in that the (third) supply contrast ΔV3S3 during the subsequent rotation operation S3 is made smaller than that during image formation (S2).

[0100] Table 4 shows the measurement (comparison) results of the development fog density (%) in Example 2. For reference, the measurement in Example 1 is also shown together.

[0101]

Table 4

[0102] As shown in Table 4, in Example 2, it was confirmed that the development fogging was significantly improved from the first rotation of the developing roller compared to Example 1.

[0103] This is presumably because by reducing the supply contrast during the "post-rotation operation" after the image formation operation and reducing the toner coat amount on the developing roller 42, the toner coat amount on the developing roller 42 during the "pre-rotation operation" in the next image formation operation can be reduced. su It is presumed that this is because it can be achieved.

[0104] Also, by reducing the toner coat amount on the developing roller 42 during the pre-rotation operation, the effects of reducing the amount of toner contacting the photosensitive drum itself and increasing the contact opportunity per grain with the developing blade 44 can be obtained simultaneously. Therefore, in Example 2, it is presumed that the development fogging was significantly improved from the first rotation of the developing roller.

[0105] Thus, even in a configuration where the developing roller 42 and the photosensitive drum are always in contact, by adjusting the output setting of the voltage, the transfer of toner to the photosensitive drum (the "development fogging" phenomenon) during the "pre-rotation operation" before starting the image formation operation can be effectively suppressed. In particular, as described above, Example 2 can more effectively suppress the transfer of toner to the photosensitive drum than Example 1.

[0106] The present invention can be summarized as follows.

[0107] (1) The image forming apparatus (M) of the present invention An image carrier (1) that carries an electrostatic latent image on its surface, A developer carrier (42) that contacts the surface of the image carrier and carries a developer on its surface for performing an image forming operation (S2) for developing the electrostatic latent image to form an image, A supply member (43) that supplies the developer to the developer carrier, A regulating member (44) that triboelectrically charges the developer carried on the surface of the developer carrier and regulates the layer thickness of the developer, a first voltage applying means (50) for applying a voltage to the developer carrier, and a second voltage applying means (51) for applying a voltage to the supply member.

[0108] The image forming apparatus successively performs a pre-rotation operation (S1) of rotating the image carrier and the developer carrier in contact with each other before the image forming operation, and an image forming operation (S2).

[0109] The image forming apparatus has a control means (C) for controlling the first voltage applying means and the second voltage applying means. When performing the image forming operation (S2), the difference (V3 - V4) between the voltage (V3) applied to the developer carrier by the first voltage applying means and the voltage (V4) applied to the supply member by the second voltage applying means is defined as the first supply contrast (ΔV1S2). When performing the pre-rotation operation (S1), when the difference (V3 - V4) between the voltage (V3) applied to the developer carrier by the first voltage applying means and the voltage (V4) applied to the supply member by the second voltage applying means is defined as the second supply contrast (ΔV2S1), the control means controls the second supply contrast to be smaller than the first supply contrast or to have a polarity opposite to that of the first supply contrast.

[0110] Thereby, the charge of the developer carried on the developer carrier during the pre-rotation operation is more easily maintained normally, and the amount of developer transferred from the developer carrier to the image carrier is effectively suppressed.

[0111] (2) In the image forming apparatus of the present invention, after the image forming operation, a post-rotation operation (S3) of rotating the image carrier and the developer carrier in contact with each other may be successively performed.

[0112] When performing the backward rotation operation (S3), when the difference between the voltage (V3) applied to the developer carrier by the first voltage application means and the voltage (V4) applied to the supply member by the second voltage application means is defined as the third supply contrast (ΔV3S3), The control means may control the third supply contrast to be smaller than the first supply contrast or to have a polarity opposite to that of the first supply contrast.

[0113] Thereby, the amount of the developer supplied from the supply member to the developer carrier during the backward rotation operation can be suppressed. As a result, when performing the next image formation, the charge of the developer carried on the developer carrier during the forward rotation operation is likely to be normally maintained, and the amount of the developer transferred from the developer carrier to the image carrier is also effectively suppressed.

[0114] (3) In the image forming apparatus of the present invention, When performing the backward rotation operation (S3), the surface potential (V2) of the image carrier (1) can be set to zero.

[0115] (4) In the image forming apparatus of the present invention, When performing the backward rotation operation (S3), the third supply contrast (ΔV3S3) can be set to zero.

[0116] (5) In the image forming apparatus of the present invention, When performing the forward rotation operation (S1), the surface potential (V2) of the image carrier (1) can be set to zero.

[0117] (6) In the image forming apparatus of the present invention, When performing the forward rotation operation (S1), the second supply contrast (ΔV2S1) can be set to zero.

[0118] (7) Another image forming apparatus (M) of the present invention includes an image carrier (1) that carries an electrostatic latent image on its surface, a developer carrier (42) that comes into contact with the surface of the image carrier and carries a developer on its surface for performing an image forming operation (S2) for developing the electrostatic latent image to form an image, A supply member (43) for supplying developer to a developer carrier, a regulating member (44) for triboelectrically charging the developer carried on the surface of the developer carrier and regulating the layer thickness of the developer, a first voltage applying means (50) for applying a voltage to the developer carrier, and a second voltage applying means (51) for applying a voltage to the supply member.

[0119] The image forming apparatus continuously performs an image forming operation (S2) and a post-rotation operation (S3) of rotating the image carrier and the developer carrier in contact with each other after the image forming operation.

[0120] The image forming apparatus has a control means (C) for controlling the first voltage applying means and the second voltage applying means. When performing the image forming operation (S2), a difference (V3 - V4) between the voltage applied to the developer carrier by the first voltage applying means and the voltage applied to the supply member by the second voltage applying means is defined as a first supply contrast (ΔV1S2). When performing the post-rotation operation (S3), when a difference (V3 - V4) between the voltage applied to the developer carrier by the first voltage applying means and the voltage applied to the supply member by the second voltage applying means is defined as a third supply contrast (ΔV3S3), the control means controls the third supply contrast to be smaller than the first supply contrast or to have a polarity opposite to that of the first supply contrast.

[0121] (8) In the image forming apparatus of the present invention, when performing the post-rotation operation (S3), the surface potential (V2) of the image carrier (1) can be set to zero.

[0122] (9) In the image forming apparatus of the present invention, when performing the post-rotation operation (S3), the third supply contrast (ΔV3S3) can be set to zero.

[0123] (10) In the image forming apparatus of the present invention, the control means In the previous rotation operation (S1), immediately before the image forming operation (S2) starts, the surface of the image carrier potential (V2) can be controlled (S1a) to change stepwise.

[0124] (11) In the image forming apparatus of the present invention, The control means In the previous rotation operation (S1), immediately before the image forming operation (S2) starts, The voltage applied to the developer carrier by the first voltage applying means is changed stepwise, Control (S1b, S1c) can be performed to change stepwise the voltage applied to the supply member by the second voltage applying means (51).

[0125] (12) In the image forming apparatus of the present invention, The control means In the subsequent rotation operation (S3), after the image forming operation (S2) ends immediately after to the surface of the image carrier potential (V2) can be controlled (S3a) to change stepwise.

[0126] (13) In the image forming apparatus of the present invention, The control means In the subsequent rotation operation (S3), immediately after the image forming operation (S2) ends, The voltage applied to the developer carrier by the first voltage applying means (50) is changed stepwise, Control (S3b, S3c) can be performed to change stepwise the voltage applied to the supply member by the second voltage applying means (51).

[0127] (14) In the image forming apparatus of the present invention, The developer remaining on the surface of the image carrier after the developer image is transferred from the image carrier may be collected by the developer carrier.

Explanation of Signs

[0128] 1 Photoconductor drum (image carrier) 42 Developing roller (developer carrier) 43 Supply roller (supply member) 44 Developing blade (restricting member) 50 Developing voltage power supply (first voltage applying means) 51 Supply voltage power supply (second voltage applying means) C Control unit (control means) M Image forming apparatus S1 Previous rotation operation S2 Image forming operation V3 Developing voltage V4 Supply voltage ΔV1S2 First supply contrast ΔV2S1 Second supply contrast

Claims

1. An image carrier that carries an electrostatic latent image on its surface, A charging member that charges the surface of the image carrier, A developer carrier that contacts the surface of the image carrier and carries a developer charged to a normal polarity on its surface to perform an image forming operation of developing the electrostatic latent image to form an image, A supply member that contacts the surface of the developer carrier and supplies the developer to the developer carrier, Charging voltage applying means for applying a charging voltage to the charging member, Developing voltage applying means for applying a developing voltage to the developer carrier, Control means for controlling the charging voltage applying means and the developing voltage applying means, and having, The control means controls to be capable of executing the image forming operation and a first rotation operation executed before the image forming operation. When starting the first rotation operation, the surface of the image carrier and the surface of the developer carrier are in contact with each other. In the first rotation operation, the charging voltage less than the discharge start voltage is applied to the charging member, and the surface of the image carrier and the surface of the developer carrier are rotated in a contact state, When performing the image forming operation, a potential difference formed between the developer carrier and the supply member is defined as a first potential difference, When performing the first rotation operation, when a potential difference formed between the developer carrier and the supply member is defined as a second potential difference, The control means performs control so that the second potential difference becomes smaller than the first potential difference in the first rotation operation. An image forming apparatus characterized by this.

2. After the image forming operation, a second rotation operation of rotating the image carrier and the developer carrier in a contact state is subsequently performed, When performing the second rotation operation, when a potential difference formed between the developer carrier and the supply member is defined as a third potential difference, The control means performs control so that the third potential difference becomes smaller than the first potential difference. The image forming apparatus according to claim 1, characterized by this.

3. When performing the second rotation operation, the surface potential of the image carrier is zero. The image forming apparatus according to claim 2, characterized by this.

4. When performing the second rotation operation, the third potential difference is zero. The image forming apparatus according to claim 2 or 3, characterized by this.

5. When performing the first rotation operation, the surface potential of the image carrier is zero. The image forming apparatus according to any one of claims 1 to 4, characterized by this.

6. When performing the first rotational operation, the second potential difference is zero, and the image forming apparatus according to any one of claims 1 to 5, characterized in that.

7. An image carrier that carries an electrostatic latent image on its surface, A developer carrier that is in contact with the surface of the image carrier and carries a developer charged to a normal polarity on its surface for performing an image forming operation of developing the electrostatic latent image to form an image, A supply member that is in contact with the surface of the developer carrier and supplies the developer to the developer carrier, Developing voltage applying means for applying a developing voltage to the developer carrier, Control means for controlling the developing voltage applying means, and having, The control means is controllably configured to execute the image forming operation and a second rotational operation executed after the image forming operation, and in the second rotational operation, the surfaces of the image carrier and the developer carrier are rotated in a state of being in contact with each other to execute a stop operation, When performing the image forming operation, the potential difference formed between the developer carrier and the supply member is defined as a first potential difference, When performing the second rotational operation, when the potential difference formed between the developer carrier and the supply member is defined as a third potential difference, The control means performs control such that the third potential difference is smaller than the first potential difference in the second rotational operation while applying the developing voltage having a polarity opposite to the normal polarity to the developer carrier. The image forming apparatus, characterized in that.

8. When performing the second rotational operation, the surface potential of the image carrier is zero, and the image forming apparatus according to claim 7, characterized in that.

9. The control means, In the first rotational operation, immediately before the start of the image forming operation, control is performed to gradually change the surface voltage of the image carrier, and the image forming apparatus according to any one of claims 1 to 6, characterized in that.

10. The control means, In the first rotational operation, immediately before the start of the image forming operation, Control is performed to gradually change the voltage applied to the developer carrier by the developing voltage applying means, and the image forming apparatus according to claim 9, characterized in that.

11. The control means, In the second rotational operation, immediately before the end of the image forming operation, control is performed to gradually change the surface voltage of the image carrier, and the image forming apparatus according to any one of claims 2, 3, 4, 7, and 8, characterized in that.

12. The control means, In the second rotation operation, immediately before the image forming operation ends, control is performed to gradually change the voltage applied to the developer carrier by the developer voltage applying means, The image forming apparatus according to claim 11, characterized in that.

13. The developer remaining on the surface of the image carrier after the developer image is transferred from the image carrier is recovered by the developer carrier, The image forming apparatus according to any one of claims 1 to 12, characterized in that.

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