JP2013041219A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces an influence associating with application of discharge voltage on transfer current during image formation and supplies appropriate transfer current during reduced-interval transfer control.SOLUTION: A discharge power supply 8 has a discharge power supply reference point D3 that is a standard of voltage applied to discharge means 9 connected with the discharge power supply 8. A transfer power supply 7 has a transfer power supply reference point A3 that is a standard for voltage applied to transfer means 5 connected with the transfer power supply 7. A transfer current detection unit 7c is connected to the transfer power supply reference point A3, and the discharge power supply reference point D3 is connected with the transfer power supply reference point A3 directly without passing through the transfer current detection unit 7c.

Description

  The present invention provides a transfer unit that transfers a toner image formed on an image carrier onto a recording material, and a separation unit that separates the recording material electrostatically attracted to the image carrier from the image carrier. The present invention relates to a type image forming apparatus.

  An image forming apparatus such as an electrophotographic laser beam printer (LBP) or a copying machine forms and supports a toner image on the surface of an image carrier based on image information, and transfers and fixes the image onto a recording material such as paper. By doing so, it is output as an image formed product (copy, print).

  In particular, in an image forming apparatus that forms an image by applying a constant voltage to a transfer unit, when a current value necessary for image transfer is applied to the transfer unit, it may be determined based on a voltage value generated in the transfer unit. .

  There are various means, but one is a transfer voltage contact method disclosed in Patent Document 1.

  In this method, the transfer power source is controlled so that a transfer current value applied to a transfer roller as a transfer unit becomes a preset value between non-image areas or between recording sheets. This method can supply a current suitable for transferring a toner image even if a characteristic change caused by a change in the surrounding environment of the transfer roller or a change due to other factors occurs.

  In addition to these controls, there may be a case where a charge eliminating means such as a charge eliminating needle is provided to separate the recording material from a transfer belt (transfer roller) as an image carrier or an intermediate transfer member. As shown in Japanese Patent Application Laid-Open No. H10-260260, a charge removing unit using a corona discharger is disposed downstream of the recording material conveyance direction, and the charge generated by the corona discharge immediately after being discharged from the transfer portion. One example is an image forming apparatus that irradiates particles.

Japanese Patent Application Laid-Open No. 11-95581 JP 2002-372874 A

  However, as shown in Patent Document 1, there is a case where the above-described transfer voltage determination method cannot be applied to a configuration including a transfer unit and a charge removal unit.

  That is, in the configuration disclosed in Patent Document 1, it is necessary to dispose the charge eliminating unit and the transfer unit in proximity. Here, since the voltage applied to the charge eliminating unit and the transfer unit is a reverse potential, the potential difference becomes larger. For this reason, a part of the charged particles generated by the static elimination unit flows into the transfer unit, so that a leakage current is generated and the current that is originally required by the transfer unit cannot be obtained. Therefore, the optimum voltage to be applied cannot be applied. .

  FIG. 1 is an overall configuration diagram of an electrophotographic image forming apparatus, and FIG. 2 is a schematic diagram of a connection configuration between a transfer power source and a neutralization power source in a conventional configuration.

  In this example, the electrophotographic photosensitive member 1 as an image carrier is of a rotating drum type (hereinafter referred to as “photosensitive drum”) provided with a photosensitive layer on the surface. Around the photosensitive drum 1, a charging device 2, a roller-shaped contact transfer member (hereinafter referred to as “transfer roller”) 5 as a transfer unit, and a charge removal needle 9 as a charge removal unit are provided. A high voltage circuit 6 for supplying a voltage to the static elimination needle 9 is disposed. Then, the recording paper P as a recording material is nipped and conveyed in the direction of the arrow by the photosensitive drum 1 and the transfer roller 5.

  As shown in FIG. 1, at present, the transfer power supply 7 and the charge removal power supply 8 are independently arranged. In this configuration, the flow of current flowing through the transfer power supply 7 and the charge removal power supply 8 will be described with reference to FIG.

  The current flow differs between the image area (during printing operation) and the non-image area (between paper or pre-rotation). The transfer current during the printing operation passes from the positive transfer power source through the resistor 118 indicating the transfer roller 5, and passes through the grounding portion, the current detection resistor 115, the negative transfer power source reference point A1, the negative transfer resistor 108, and the positive transfer power source reference point B1. There is a path 1 that returns to the positive transfer power source. Further, the transfer current has a path 2 that flows to the grounding portion through a conveyance guide or the like using the recording paper P that is nipped and conveyed from the positive transfer power source as a conductive medium. A path using the recording paper P as a conductive medium also exists between the static elimination power source 8, the transfer roller 5 and the static elimination needle 9. One is a path 3 that passes from the static elimination needle 9 through the recording paper P to the grounding portion, the current detection resistor 115, the transfer negative power supply reference point A1, the transfer negative resistance 108, and the transfer positive power supply reference point B1 to return to the transfer positive power supply. is there. Further, a path 4 returns from the transfer roller 5 to the transfer positive power supply through the recording paper P as a medium through the static elimination power supply 8, the static elimination power supply reference point D1, the transfer negative power supply reference point A1, the transfer negative resistance 108, and the transfer positive power supply reference point B1. is there.

  Next, the flow of current between the sheets. When the transfer voltage and the static elimination voltage are applied simultaneously, a leakage current is generated between the transfer roller 5 and the static elimination needle 9 as described above. Therefore, the transfer current passes through the resistor 118 indicating the transfer roller 5 from the positive transfer power source. , Ground 5, transfer current detection resistor 115, transfer negative power supply reference point A 1, transfer negative resistance 108, transfer positive power supply reference point B 1, path 5 returning to the transfer positive power supply, and leakage from the transfer positive power supply to the static elimination needle 9 The grounding part connected to the static elimination resistor 112 and the static elimination power supply reference point D1 via the pseudo resistance 117 indicating the current, and again from the grounding part, the current detection resistor 115, the transfer negative power supply reference point A1, the transfer negative resistance 108, and the transfer positive power supply reference point There are two types of paths 6 that return to the positive transfer power source via B1.

  Since the path 6 passes through the transfer current detection unit, that is, the current detection resistor 115, the leakage current generated between the transfer roller 5 and the static elimination needle 9 is added to the value of the current flowing through the transfer circuit. In addition, a voltage drop due to leakage current passing through the transfer negative resistance 108 is also affected. Therefore, the transfer voltage determination method cannot be applied correctly.

  Implementation of the transfer voltage contact method takes time. The time may be longer than the paper interval time determined by the recording paper interval and a predetermined peripheral speed (process speed). In this case, measures may be taken such as extending the interval between sheets, but the printing amount per unit time, that is, throughput must be reduced.

  Here, as shown in Patent Document 1, a method of reducing the effect of leakage current by reducing the static elimination voltage at the timing of current detection is also conceivable. However, in this case, with the recent increase in the speed of the image forming apparatus, there is the following problem when “small paper gap control” is performed in which the gap between recording papers is reduced to improve the productivity. That is, there is a restriction that the transfer voltage contact method is performed at a timing when the transfer site is a non-image area and the voltage level applied to the charge removal needle as the charge removal means is low. For this reason, it is necessary to continue to apply a static elimination voltage for improving the recording paper separation property in the small paper gap control between the paper sheets, which is not applicable due to an increase in leakage current.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of reducing an influence on a transfer current accompanying application of a static elimination voltage at the time of image formation, and supplying an appropriate transfer current even at the time of small paper sheet control.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention
Transfer means for transferring a toner image formed on the image carrier to a recording material;
A neutralizing unit disposed downstream of the transfer unit with respect to the moving direction of the recording material, for neutralizing and separating the recording material electrostatically attracted to the image carrier;
A transfer power supply for supplying a voltage to the transfer means;
A static elimination power source for supplying a voltage to the static elimination means;
A transfer current detector for detecting a current value flowing through the transfer means;
A control unit for controlling the voltage of the transfer power source based on the current value detected by the transfer current detection unit;
In an image forming apparatus having
The neutralization power source has a neutralization power source reference point that serves as a reference for a voltage applied to the neutralization unit connected to the neutralization power source, and the transfer power source is a reference for a voltage applied to the transfer unit connected to the transfer power source Has a transfer power reference point
The transfer current detection unit is connected to the transfer power supply reference point,
The image forming apparatus is characterized in that the static elimination power supply reference point is directly connected to the transfer power supply reference point without passing through the transfer current detection unit.

  According to the present invention, it is possible to accurately detect the transfer current value to be applied to the transfer unit even when a leakage current is generated between the transfer unit (for example, the transfer roller) and the charge removal unit (for example, the charge removal needle). Regardless of the occurrence of leakage current, it is possible to set the transfer voltage appropriately.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is the schematic explaining the connection form of the transfer power supply and static elimination power supply in a conventional structure. It is a figure explaining the operation | movement process of the image forming apparatus which concerns on this invention. FIG. 3 is a schematic diagram of a connection form between a transfer power source and a charge removal power source in the first embodiment of the present invention. It is a transfer power supply circuit diagram. It is a static elimination power supply circuit diagram. 6 is an output time chart of a transfer power source and a neutralization power source in the inter-sheet conveyance control. 6 is an output time chart of a transfer power source and a neutralization power source in conveyance control between small papers. It is the connection form schematic of the transfer power supply and static elimination power supply in 2nd Example of this invention.

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

Example 1
FIG. 1 shows the overall configuration of an embodiment of an image forming apparatus according to the present invention. In this embodiment, the image forming apparatus applies an electrophotographic process and uses a contact transfer method, an ATVC method, and a charge eliminating method for a recording material using a charge eliminating needle.

(1) Image Forming Process Referring to FIG. 1, in this embodiment, as described above, the image forming apparatus is a rotating drum type electrophotographic photosensitive member provided with a photosensitive layer on the surface as an image carrier. A photosensitive drum 1 is provided. Around the photosensitive drum 1, a roller-shaped charging device as a charging means, that is, a charging roller 2, a developing device 4 provided with a developing sleeve 4a as a developing means, and a roller-shaped contact transfer member as a transfer means, that is, A transfer roller 5 and a static elimination needle 9 as a static elimination means are provided. Further, around the photosensitive drum 1, a cleaning device 12 as a cleaning means for the photosensitive drum 1 is disposed.

  The image forming process will be described with reference to FIG. The photosensitive drum 1 is rotationally driven in the direction of the arrow at a predetermined peripheral speed (process speed), and the following image forming processes (a) to (g) are applied.

(A) Charging:
The surface of the rotationally driven photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging device (charging roller) 2.

(B) Exposure:
Next, as the image information writing means on the charging processing surface, image exposure 3 is performed by an image exposure means (not shown), whereby the charged potential of the bright exposure area is attenuated, and the surface of the photosensitive drum 1 corresponds to the exposure image information. An electrostatic latent image is formed. The image exposure means is a scanning exposure device for an image-modulated laser beam, a projection exposure device for a document image, or the like.

(C) Development:
The electrostatic latent image on the photosensitive drum 1 is sequentially visualized as a toner image (visualized image) by the developing sleeve 4 a of the developing device 4.

(D) Transcription:
The transfer means in this embodiment is a contact-type transfer means using a roller-like contact transfer member, that is, a transfer roller 5. The toner image is transferred onto the recording paper P as a recording material by the transfer roller 5 at the transfer site T (transfer nip, pressure nip between both the photosensitive drum 1 and the transfer roller 5).

  The transfer roller 5 has a metal cored bar 5a and a conductive elastic layer formed in a roller shape around the cored bar. The transfer roller 5 is pressed against the photosensitive drum 1 against the elasticity of the elastic layer with a predetermined pressing force to form a transfer portion T. The transfer roller 5 rotates in the forward direction with respect to the rotation of the photosensitive drum 1. It rotates at the same peripheral speed as the speed.

  The recording sheet P is fed from a sheet feeding unit (not shown), and is fed to the transfer part T at a predetermined control timing through a registration roller / transfer guide (not shown) disposed on the front side of the transfer part T. Is done. The registration roller moves the recording paper P so that when the leading edge of the toner image formed on the surface of the photosensitive drum 1 reaches the transfer site T, the leading edge of the recording paper P reaches the transfer site T at the same time. Feed to the transfer site T.

  The recording paper P fed to the transfer portion T is transported while sandwiching the transfer portion T with its surface in close contact with the photosensitive drum 1. Also, during the period from when the leading end of the recording paper P reaches the transfer site T until the trailing edge exits the transfer site T, the transfer roller 5 is connected to the transfer power source (high voltage power source 6) via the cored bar 5a. A predetermined transfer voltage is applied from the transfer bias applying means 7. The transfer voltage is a potential having a polarity opposite to the charging polarity of the toner image. In the process in which the recording paper P is nipped and conveyed across the transfer portion T, the toner image on the photosensitive drum 1 side is moved to the recording paper P side by the action of the transfer electric field formed by the transfer roller 5 and the pressing force at the transfer portion T. Sequentially transferred.

  In this embodiment, the transfer voltage setting similar to that of Patent Document 1 is performed. Specifically, the transfer power source is controlled so that a transfer current value applied to a transfer roller as a transfer unit becomes a preset value between non-image areas or between recording sheets. Hereinafter, this method will be described as an ATVC method.

(E) Separation:
The recording paper P that has passed through the transfer portion T is electrostatically adsorbed on the surface of the photosensitive drum 1. Therefore, the discharge needle 9 is arranged on the recording paper discharge side of the transfer portion T, that is, downstream of the transfer roller 5 with respect to the moving direction of the recording paper P and adjacent to the transfer roller 5 as a recording material discharging means. Has been established. The discharge of the recording paper P that is electrostatically attracted to the surface of the photosensitive drum 1 through the transfer member position T by the static elimination needle 9 facilitates the separation of the recording paper P from the photosensitive drum 1.

  The top of the static elimination needle 9 is located slightly below the transfer site T, and a predetermined static elimination voltage (potential having a polarity opposite to the transfer voltage for the transfer roller 5) is applied to the static elimination needle 9. The charge removal voltage is supplied from a charge removal power supply (charge removal bias applying means) 8 in the high voltage power supply 6.

(F) Fixing:
The recording paper P leaving the transfer portion T and separated from the surface of the photosensitive drum 1 is guided by the conveyance guide 10 and introduced into the fixing device 11, and the transferred toner image is fixed on the recording paper surface as a permanently fixed image. Processed and discharged as an image formed product (copy, print).

(G) Cleaning:
The surface of the photosensitive drum 1 from which the recording paper P has been separated is cleaned by the cleaning device 12 after removal of deposits such as residual toner and paper dust, and is repeatedly used for image formation.

  As an image forming method, for example, there is a regular development method in which a charged photoconductor surface is exposed to a background portion of image information (background exposure method) and a portion other than the background portion is developed. On the other hand, there is a reversal development method in which the image information portion is exposed (image exposure method) and the non-exposed portion is developed, and each of the features is used.

  In the image forming apparatus of the present embodiment, the polarity of the charging process by the primary charging device 2 of the photosensitive drum 1 which is an image carrier is negative. The toner development by the developing device 4 for the electrostatic latent image formed on the surface of the photosensitive drum 1 is a reversal developing method using negative toner (negative toner) having the same polarity as the charging processing polarity of the photosensitive drum 1. . A thin layer of toner is coated on a developing sleeve 4a rotatably attached to the developing device 4, and a predetermined developing voltage is applied to the developing sleeve 4a from an external power source (developing voltage application power source) (not shown). As a result, the toner on the developing sleeve 4a is selectively transferred to the photosensitive drum 1 side with respect to the electrostatic latent image, and the electrostatic latent image is reversely developed with the toner. The transfer voltage is a positive potential, and the charge removal voltage is a negative potential. The transfer power supply 7 and the charge removal power supply 8 will be described later.

(2) Printer Operation Process FIG. 3 is an operation diagram of the image forming apparatus of this embodiment, that is, a printer. The following A to G show the operation steps of the printer.

  A. Pre-multi-rotation stroke: This is a period (printer warm-up period) for driving each actuator to drive the photosensitive drum 1 for a predetermined time after the printer power is turned on, and for the required process equipment to perform a preparatory operation. . The fixing device 11 is raised to a predetermined temperature during this period.

  B. Ready state (standby control): When the fixing device 11 rises to a predetermined temperature and the predetermined multi-rotation stroke is completed, the drive of each actuator is stopped if there is no print request, and the printer waits until there is a print request. It becomes. In this ready state, the fixing device 11 enters standby control and is maintained at a predetermined standby temperature.

  C. Pre-rotation process: This is a period in which, when there is a print request from the ready state, each actuator is restarted to rotate the photosensitive drum 1, and the pre-printing operation is executed by the required process equipment until the start of printing. In this pre-rotation stroke, the fixing device 11 is heated to a predetermined temperature at which fixing can be performed.

  D. Printing process: When the pre-rotation process is completed, each actuator is continuously driven, and the first printing operation is executed. In the case of the continuous printing mode, the printing operation is repeated and printing processes for a predetermined set number n are sequentially performed.

  E. Inter-sheet process: In the continuous print mode, for example, after the trailing edge of the first recording paper P1 passes through the transfer site T, the non-passage in the transfer section until the leading edge of the next recording paper P2 reaches the transfer site T. It is a paper period, and continues with P3 and P4 according to the number of prints.

  F. Post-rotation process: This is a period during which an operation for shifting to the ready state is performed, for example, the driving of each actuator is continued for a while after the printing operation process is completed, and the photosensitive drum 1 is cleaned.

  G. Ready state (standby control): When a predetermined post-rotation stroke is completed, the driving of each actuator is stopped, and the printer enters a ready state in which it waits for a next print request. At this time, the fixing device 11 enters standby control and is maintained at a predetermined standby temperature.

  In the above, if there is a print request immediately after the pre-multi-rotation stroke, the process continues to the pre-rotation process and printing is performed as it is.

(3) Transfer Circuit / Static Removal Circuit The configuration of a transfer power supply circuit (transfer circuit) that generates a transfer voltage applied to the transfer roller 5 and a charge removal power supply circuit (charge removal circuit) that generates a charge removal voltage applied to the charge removal needle 9 are as follows. 1 and 2 will be described. FIG. 4 shows a connection form of the transfer power supply 7 and the charge removal power supply 8 in this embodiment. As will be described in detail later, as shown in FIG. 4, in this embodiment, the transfer power source 7 includes a transfer positive power source 7a that generates a positive voltage and a transfer negative power source 7b that generates a negative voltage. Yes. Further, a transfer positive power source 7a and a transfer negative power source 7b are connected in series to the transfer means (transfer roller) 5 in the order of the transfer roller 5, the transfer positive power source 7a, and the transfer negative power source 7b. Further, a transfer negative power supply reference point A3, which serves as a reference for a connection point voltage between the transfer negative power supply 7b and the transfer positive power supply 7a, is connected to a current detector 7c that detects a current flowing through the transfer power supply 7.

1: Transfer Circuit FIG. 5 is a transfer power supply circuit diagram. In this embodiment, the transfer power supply 7 is constituted by the transfer positive circuit of the transfer positive power supply 7a and the transfer negative circuit of the transfer negative power supply 7b as described above, and the transfer voltage is output from the output terminal 205. The output terminal 205 is connected to the transfer roller 5 so that a high voltage bias can be applied to the transfer roller 5.

  The configuration of the transfer circuit will be described below.

  The circuit is controlled by control signals CLK1 / CLK2 and CNT1 / CNT2 output from the CPU 13 constituting the control unit, and can output a transfer voltage at a desired timing and a desired level. An analog signal SNS corresponding to the level of the transfer current flowing from the output terminal 205 is output from the transfer circuit 7 and input to the analog / digital terminal of the CPU 13. That is, the CPU 13 can detect the transfer current.

  A voltage adjusted by a transistor 211 described later is applied to the primary winding of the step-up transformer 201. When the clock CLK1 output from the CPU 13 is output, the step-up transformer 201 is driven by the switching operation of the FET 210, and a high-voltage AC voltage is generated in the secondary winding. The generated high-voltage AC voltage is rectified by the diode 202, the capacitor 204, and the resistor 219, and a positive DC voltage (transfer positive voltage) is generated at the output terminal 205. The voltage at the output terminal 205 is divided by resistors 203, 217, and 218 and connected to the negative input of the operational amplifier 214. This is a transfer positive circuit (transfer positive power supply) 7a.

  Further, the configuration and operation of the circuit controlled by the control signals CLK2 and CNT2 output from the CPU 13 are the same as those described above, but the diode 202 'is reversed with respect to the diode 202. A DC voltage (transfer negative voltage) is generated. This is a transfer negative circuit (transfer negative power source) 7b.

  As described above, the transfer positive power supply (transfer positive circuit) 7a and the transfer negative power supply (transfer negative circuit) 7b have the same configuration and operation. Therefore, the transfer positive circuit of the transfer positive power supply 7a will be described as a representative. To do.

  The CNT1 signal is a pulse signal that has been subjected to pulse width modulation (PWM), and is DC-converted by a low-pass filter including a resistor 216 and a capacitor 215 and input to the positive input of the operational amplifier 214. The operational amplifier 214 compares the voltage level of the output terminal 205 with the target value set by the DUTY ratio of the CNT1 signal. When the voltage level of the output terminal 205 is lower than the target value, the output terminal voltage of the operational amplifier 214 increases and the base current of the transistor 212 increases, so that the voltage applied to the step-up transformer 201 increases. As a result, the voltage at the output terminal 205 rises. When the voltage level of the output terminal 205 is higher than the target value, the voltage at the output terminal of the operational amplifier 214 decreases, and the base current of the transistor 212 gradually decreases, so that the voltage applied to the step-up transformer 201 decreases. As a result, the voltage level of the output terminal 205 decreases. With such an operation, the voltage level of the output terminal 205 can be controlled by the CNT signal. That is, constant voltage control is possible.

  Next, the transfer current detection unit 7c will be described.

  The transfer current detection is detected by a circuit (transfer current detection unit) 7c including an operational amplifier 209 and resistors 208, 206, and 207 connected to the fifth terminal side of the step-up transformer 201.

The positive input of the operational amplifier 209, the power supply voltage: V _cc is the voltage divided by the resistors 206 and 207: V _t (transfer voltage) is input. When the voltage at the output terminal 205 rises due to the drive of the step-up transformer 201, a current having a level equivalent to the current output from the output terminal 205 flows through the resistor 208. As a result, a voltage is generated across the resistor 208, and the output of the operational amplifier 209, that is, the SNS signal has the following voltage level.
SNS = Vt + Rs × Io (Formula 1)
Here, R _s is the resistance value of the resistor R 208, and I _o is the current value output from the output terminal 205.

  The relationship between the voltage level of the SNS and the current output from the output terminal 205 is stored in advance in a storage device (not shown) in the CPU 13. Constant voltage control is possible by adjusting the CNT signal according to the SNS signal.

2: Static elimination circuit FIG. 6: is a static elimination power supply circuit diagram. The basic configuration of the circuit of the static elimination power source 8 (static elimination circuit) is the same as that of the transfer negative circuit (transfer negative power source) 7b of the transfer power source 7, and the circuit operation is also the same. In the static elimination power supply circuit diagram, circuit components that are the same as those of the transfer power supply 7 are given the same two-digit reference numbers as the circuit components of the transfer power supply 7 in the order of 400.

  As described above, the basic configuration of the static elimination power source 8 is the same as that of the transfer negative circuit, and the transfer power source 7 and the static elimination power source 8 generate contradictory voltages.

  That is, the static elimination voltage is output from the output terminal 405. The output terminal 405 is connected to the static elimination needle 9 so that a high voltage bias can be applied to the static elimination needle 9. The static elimination circuit is controlled by control signals CLK3 and CNT3 output from the CPU 13, and can output a static elimination voltage at a desired timing and a desired level.

(4) Transfer power source control / static discharge power source control 1: Control during long paper interval A control method of the transfer power source 7 and the neutralization power source 8 during long paper interval will be described below. FIG. 7 is a timing chart for explaining the circuit operation of FIG. 4 during the long paper interval control.

  In the image forming apparatus according to the present embodiment, it is difficult to suppress variation in resistance when the conductive transfer roller 5 is manufactured, and the resistance value is changed due to change in ambient temperature or deterioration of durability. On the other hand, when the transfer bias is set to constant current control, the transfer voltage fluctuates depending on the printing ratio of the image to be transferred and optimal transfer cannot be performed. For this reason, this problem is avoided by using the ATVC method.

ATVC is performed mainly during non-image formation and when no static elimination voltage is applied (paper interval: area A). The transfer power source 7 is controlled so that the current flowing through the transfer roller 5 has a preset constant current value I ₀ (constant current mode), and the applied voltage V _t0 at this time is detected. The transfer voltage V _t is determined from the detected value of the applied voltage V _t0 .

For example, the transfer voltage V _t is calculated and determined using the following calculation formula.
Vt = a × Vto + b (Formula 2)
A and b described in Equation 2 are constants for determining the voltage value, and are stored in advance in a storage device (not shown) in the CPU 13.

In this manner, by applying a transfer voltage V _t of the decision in the transfer site image area (during sheet passing) to the transfer roller 5 a constant voltage control, executes the transfer of the toner image from the photosensitive drum 1 to the recording paper P Let

  When the image forming apparatus that has received the print request starts the pre-rotation process, the transfer power supply 7 starts up in the constant current mode (section A1). Next, immediately before the leading edge of the first recording paper P1 reaches the transfer site T, the transfer power source 7 is driven in the constant voltage mode. At this time, the separation between the leading edge of the recording paper P1 and the transfer roller 5 is improved. Therefore, a static elimination voltage is temporarily applied to the static elimination needle 9 (section B). During image transfer to the recording paper P1, the transfer voltage rises to an optimal value while maintaining the constant voltage mode (section C1). In the next section (section A2), when the image transfer is completed and the recording paper P1 approaches the rear end, the transfer power source 7 switches to the constant current mode, and the rear end of the recording paper P1 and the transfer roller 5 are connected. In order to improve the separability, a static elimination voltage is temporarily applied to the static elimination needle 9. Then, immediately before the leading edge of the recording paper P2 reaches the transfer site T, a neutralizing voltage is applied to the static eliminating needle 9 again to improve the separation of the recording paper leading edge from the transfer roller 5. The recording paper P2 also passes through the image transfer section and then continues to P3 and P4.

  Next, the flow of current flowing through the transfer power source 7 and the neutralization power source 8 in the region A will be described.

  At the time of long paper control, since no static elimination voltage is applied between the papers, no leakage current flows between the transfer roller 5 and the static elimination needle 9. Therefore, the current flowing through the transfer circuit is detected at this timing. Accordingly, the transfer current passes from the positive transfer power source 7a through the resistor 318 indicating the transfer roller 5, and passes through the grounding portion, the current detection resistor 315, the negative transfer power source reference point A3, the negative transfer resistance 308, and the positive transfer power source reference point B3. There is only a path 7 that returns to the positive power source 7a. There is no path through the recording paper P that exists during the printing operation to the grounding portion because it is between the papers, because there is no conductive medium. That is, since the value of the current flowing through the transfer current detection circuit 7c becomes a value corresponding to the current flowing through the transfer roller 5, a desired ATVC can be performed.

2: Control during small paper spacing A method for controlling the transfer power supply 7 and the neutralization power supply 8 during small paper spacing will be described below. FIG. 8 is a timing chart for explaining the circuit operation of FIG.

  The basic control method is the same as the control during the long paper interval, but the driving method of the neutralization power supply 8 is different from the long paper interval control.

  During the small paper gap control, the paper gap (section A2) maintains a high static elimination voltage level. The reason for performing such control is that the neutralization voltage was applied at the timing of the trailing edge of the paper and the leading edge of the paper during the interval between the long sheets, but the off time of the neutralization voltage was lost due to the shortening of the gap between the sheets. Because it is. As described above, since the static elimination voltage is continuously applied between the sheets, a leakage current is generated between the transfer roller 5 and the static elimination needle 9. In other words, a phenomenon has occurred in which a part of the current flowing to the transfer power source 7 flows into the static elimination needle 9 adjacent to the transfer roller 5. At the time of the small paper interval, the current flowing through the transfer circuit, that is, the transfer current detector 7c is detected at this timing (region B).

  The flow of current flowing through the transfer power supply 7 and the charge removal power supply 8 in the region B will be described.

  As described above, since a leakage current is generated between the transfer roller 5 and the charge eliminating needle 9, the transfer current passes from the positive transfer power source 7a through the resistor 318 indicating the transfer roller 5, and is connected to the grounding portion, the current detection resistor 315, and the transfer. Via the negative power supply reference point A3, the transfer negative resistance 308, the transfer positive power supply reference point B3, the path 8 returning to the transfer positive power supply, and the pseudo resistance 317 indicating the leakage current from the transfer positive power supply 7a to the charge removal needle 9 There are two types of paths 9 that go back to the transfer positive power supply 7a through the resistor 312, the static elimination power supply reference point D3, the transfer negative power supply reference point A3, and the transfer negative resistance 308 transfer positive power supply reference point B3.

  Since the path 9 follows a loop-shaped path passing through the transfer power supply 7 and the charge removal power supply 8, in this example, the value of the current flowing through the transfer circuit, that is, the transfer current detection unit 7c, is the same as that between the sheets. Since the value corresponds to the current flowing through the roller 5, desired ATVC can be performed.

  In this way, the transfer power supply reference point A3 and the discharge power supply reference point D3 are connected in parallel, that is, the discharge power supply reference point D3 is directly connected to the transfer power supply reference point A3 without passing through the transfer current detection unit 7c. Is done. Thereby, since the leakage current generated between the transfer roller 5 and the static elimination needle 9 converges in the circuit without passing through the current detection unit 7c, the transfer current value to be given to the transfer roller 5 can be appropriately detected. ATVC can be applied even during the small paper interval control.

  As described in the problem, the current flow during the printing operation has four types of current paths. However, since ATVC is not applied during the printing operation, even if the current flows through the path using the recording paper as a medium. Constant voltage control is performed.

  According to the present embodiment, even when a leakage current is generated between the transfer roller 5 serving as the transfer unit and the neutralizing needle 9 serving as the charge eliminating unit, the transfer current value to be applied to the transfer roller 5 can be accurately detected. Therefore, ATVC can be appropriately performed regardless of whether or not leakage current is generated.

Example 2
The second embodiment of the present invention will be described below.

  FIG. 9 is a schematic diagram of the connection form of the transfer power supply 7 and the charge removal power supply 8 in the second embodiment. The basic configuration of the high-voltage power supply 6 in the image forming apparatus according to the second embodiment is the same as that of the first embodiment, and only the connection form of the transfer power supply 7 and the charge removal power supply 8 is different from the first embodiment.

  In other words, in the transfer power supply 7 and the charge removal power supply 8 of the first embodiment, in the first embodiment shown in FIG. 4, the circuit components are given two-digit reference numbers in the order of 300. In the transfer power supply 7 and the neutralization power supply 8, the same circuit components are given the same two-digit reference numbers in the order of 500.

  In the configuration of this embodiment, the transfer positive power supply reference point B5 and the static elimination power supply reference point D5 are connected. The flow of current flowing through the transfer power supply 7 and the charge removal power supply 8 in the region B at this time will be described.

  The transfer current passes from the transfer positive power supply 7a through the resistor 518 indicating the transfer roller 5, and passes through the grounding portion, the current detection resistor 515, the transfer negative power supply reference point A5, the transfer negative resistance 508, and the transfer positive power supply reference point B5. The transfer positive power supply 7a passes through the path 10 returning to 7a and the pseudo-resistance 517 indicating the leakage current from the transfer positive power supply 7a to the charge removal needle 9 through the charge removal resistor 512, the charge removal power supply reference point D5, and the transfer positive power supply reference point B5. It becomes the route 11 to return to.

  At this time, since the path 11 does not pass through the resistor 508 of the transfer negative power supply circuit 7b, in addition to the effect of the first embodiment, it is possible to suppress the influence on the transfer current due to the voltage drop. Therefore, since the value of the current flowing through the transfer circuit 7, that is, the transfer current detecting unit 7c is a value corresponding to the current flowing through the transfer roller 5, as in the case of the interval between long sheets, a desired ATVC can be performed. It becomes.

  According to the present embodiment, the configuration in which the leakage current does not flow into the resistance of the transfer negative power supply circuit 7b can suppress the influence of the voltage drop in the path to the transfer roller, and the transfer current applied to the transfer roller 5 Can be detected properly.

1 Photosensitive drum (image carrier)
2 Charging device (charging means)
3 Image exposure light 4 Developing device (developing means)
5 Transfer roller (transfer means)
6 High Voltage Power Supply 7 Transfer Power Supply 7a Transfer Positive Power Supply 7b Transfer Negative Power Supply 7c Transfer Current Detection Unit 8 Charge Removal Power Supply 9 Charge Removal Needle (Charge Removal Means)
13 CPU (control unit)

Claims (4)

Transfer means for transferring a toner image formed on the image carrier to a recording material;
A neutralizing unit disposed downstream of the transfer unit with respect to the moving direction of the recording material, for neutralizing and separating the recording material electrostatically attracted to the image carrier;
A transfer power supply for supplying a voltage to the transfer means;
A static elimination power source for supplying a voltage to the static elimination means;
A transfer current detector for detecting a current value flowing through the transfer means;
A control unit for controlling the voltage of the transfer power source based on the current value detected by the transfer current detection unit;
In an image forming apparatus having
The neutralization power source has a neutralization power source reference point that serves as a reference for a voltage applied to the neutralization unit connected to the neutralization power source, and the transfer power source is a reference for a voltage applied to the transfer unit connected to the transfer power source Has a transfer power reference point
The transfer current detection unit is connected to the transfer power supply reference point,
The image forming apparatus, wherein the neutralization power supply reference point is directly connected to the transfer power supply reference point without passing through the transfer current detection unit. The transfer power source includes a transfer positive power source that generates a positive voltage and a transfer negative power source that generates a negative voltage.
The transfer positive power supply and the transfer negative power supply are connected in series to the transfer means in the order of the transfer means, the transfer positive power supply, and the transfer negative power supply.
The image forming apparatus according to claim 1, wherein a transfer negative power supply reference point serving as a reference of a connection point voltage between the transfer negative power supply and the transfer positive power supply is connected to the current detection unit.   The image forming apparatus according to claim 2, wherein the static elimination power supply reference point is connected to the transfer negative power supply reference point.   The image forming apparatus according to claim 2, wherein the static elimination power supply reference point is connected to the transfer positive power supply reference point.

Images