JP4661253B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a plurality of toner image forming units each including an applied member to which an AC superimposed bias in which an AC voltage is superimposed on a DC voltage is applied.

  Conventionally, image forming apparatuses such as copying machines and printers based on electrophotography have been known. Today, color copying machines and color printers using yellow, magenta, and cyan color toners and black toners are rapidly spreading. ing.

  These color copying machines, color printers, and the like are provided with a toner image forming unit corresponding to each color in order to form a toner image for each color. Each toner image forming unit is provided with an image carrier on which a toner image is formed, a charger that charges the surface of the image carrier, a developer that supplies toner to the image carrier electrostatically, and the like. In forming an image, first, the surface of the image carrier carrying member is charged by a charger. Each toner image forming unit receives an image signal of a corresponding color, and obtains an electrostatic latent image on the surface by irradiating exposure light based on the image signal input to the surface of the image carrier after charging, The electrostatic latent image is developed with toner using a developing device to form a toner image on the surface of the image carrier. In this way, toner images corresponding to the respective colors are formed in the respective toner image forming units, and these toner images are finally transferred onto the recording medium so as to overlap each other. By fixing on the recording medium, an image composed of a fixed toner image is formed.

  A technique has been proposed in which a predetermined bias is applied to a charger or a developer provided in each toner image forming unit, and an AC superimposed bias in which an AC voltage is superimposed on a DC voltage is used as the predetermined bias (for example, , See Patent Document 1).

  FIG. 1 is a block diagram of a circuit for generating an AC superimposed bias disclosed in Patent Document 1. In FIG.

The AC superimposed bias generation circuit 8 shown in FIG. 1 is connected to each developing device 9 for yellow (Y), magenta (M), cyan (C), and black (K) toner, and is applied to each developing device 9. In order to make the control of the developing bias to be independent, an AC superimposed bias is generated independently for each color. That is, the AC superimposed bias generation circuit 8 has DC high voltage power supplies 81y, 81m, 81c, 81k for generating DC high voltages for each color, and AC voltage power supplies 82y, 82m, 82c, 82k for generating AC voltages. Are also provided for each color and also have transformers 83y, 83m, 83c, and 83k for transforming the AC voltage generated by the AC voltage power source for each color. For this reason, component cost becomes high and the mounting area of a board | substrate will also become large. Further, in the AC superimposed bias generation circuit 8 shown in FIG. 1, the AC component is asynchronous between the colors, and therefore, the distance of the signal line for each color and the distance of the load such as the resistance of the transformer provided for each color. If they are close to each other, problems relating to AC components such as voltage interference and insufficient insulation distance occur.
Japanese Patent Laid-Open No. 10-171183

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an image forming apparatus that has been devised to prevent problems relating to AC components such as voltage interference and insufficient insulation distance while reducing component cost and reducing the mounting area of a substrate. It is intended.

The image forming apparatus of the present invention that solves the above object forms an electrostatic latent image on an image carrier by charging and exposure, and develops the electrostatic latent image with toner to form a toner image on the image carrier. A plurality of toner image forming units to be formed are provided, and the toner images formed by each toner image forming unit are transferred onto the recording medium so that the toner images finally overlap each other on the recording medium, and then transferred. In an image forming apparatus for forming an image composed of a fixed toner image on the recording medium by fixing these toner images on the recording medium,
Each of the plurality of toner image forming units includes an applied member to which an AC superimposed bias in which an AC voltage is superimposed on a DC voltage is applied,
This image forming apparatus further includes
An AC voltage generator for generating AC voltage;
An AC voltage generated by the AC voltage generation unit that generates an AC voltage of the AC superimposed bias to be applied to a member to be applied to a predetermined one or a plurality of toner image forming units among the plurality of toner image forming units. A first generator that generates voltage by transforming;
A member to be applied disposed in one or more predetermined toner image forming units among the remaining toner image forming units excluding the predetermined one or more toner image forming units from the plurality of toner image forming units. The second generation is generated by transforming the AC voltage of the AC superimposed bias to be applied to the AC line applied to the connection line that electrically connects the AC voltage generator and the first generator. And
And a switching unit that switches whether or not the second generation unit generates an AC voltage.

  According to the image forming apparatus of the present invention, the first generation unit and the second generation unit generate an AC voltage of the AC superimposed bias using a common AC voltage generation unit. Therefore, the AC component is not asynchronous between colors while reducing the mounting area of the substrate, and the occurrence of problems relating to the AC component such as voltage interference and insufficient insulation distance is prevented. Further, since the switching unit is provided, the image forming apparatus of the present invention superimposes the full color mode using all the toner image forming units and the AC voltage transformed by the first generation unit on the DC voltage. Special color mode using only a toner image forming unit having an applied member to which an AC superimposed bias is applied (applied to which an AC superimposed bias on which an AC voltage transformed by the first generation unit is superimposed is applied It is possible to provide a mode in which the number of toner image forming units to be used is changed, such as a monochrome image mode in which a toner image forming unit including a member is a single toner image forming unit that forms a black toner image. Thus, it is possible to suppress excessive toner consumption and extend the life of the image carrier that is charged.

Here, the applied member is
The AC superimposing bias may be applied and the image carrier may be charged by the action of the AC superimposing bias. Alternatively, the AC superimposing bias may be applied to form an electrostatic image formed on the image carrier. A developing device that develops the latent image with toner by the action of the AC superimposed bias may be used.

  In the image forming apparatus according to the aspect of the invention, the switching unit may be provided in the middle of a path that branches from the connection line and is electrically connected to the second generation unit. It may be a switch circuit that cuts off the connection.

  For example, when the above-described full color mode is set, by turning on the switch circuit, the AC superimposed bias is applied to the applied members of all the toner image forming units, and the monochrome mode is set. In this case, the AC superimposed bias is applied only to the applied member of the toner image forming unit for forming a black toner image by turning off the switch circuit.

Furthermore, in the image forming apparatus of the present invention, the switching unit is provided with the same size as the applied AC voltage signal provided in the middle of the path branched from the connection line and electrically connected to the second generation unit. An amplifier that amplifies the amplifier and a switch circuit that grounds the output of the amplifier to the ground when turned on,
The second generation unit includes an RC circuit including a capacitor and a resistor connected in series, and an operational amplifier to which an output of the RC circuit is input, and boosts an output from the operational amplifier. May have a switch circuit that grounds the output of the RC circuit to the ground by turning on,
The second generation unit includes an RC circuit in which a capacitor is provided on the input side and a resistor connected in series to the capacitor is provided on the output side, and an operational amplifier to which an output of the RC circuit is input. Boosts the output from
The switching unit may include a switch circuit that grounds the output of the capacitor of the RC circuit to the ground when turned on, and the output of the operational amplifier may be fixed in a DC manner when the switch circuit is turned on. Or
The second generation unit includes an operational amplifier that has a negative feedback resistor and the amplification factor becomes zero when the resistor is short-circuited, and boosts the output from the operational amplifier.
The switching unit may include a switch circuit that short-circuits the resistor when turned on.

  In each of these four modes, for example, when the above-described full color mode is set, by turning off any of the above switch circuits, the AC superimposed bias is applied to the applied members of all the toner image forming units. When the above-described monochrome mode is set, any of the switch circuits is turned on so that the AC superimposed bias is applied only to the applied member of the toner image forming unit that forms a black toner image. The

  According to the present invention, it is possible to provide an image forming apparatus that has been devised to suppress problems related to AC components such as voltage interference and insufficient insulation distance while reducing component costs and reducing the mounting area of the substrate. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

  An image forming apparatus 100 shown in FIG. 2 is an image forming apparatus adopting a full color tandem system, and has a full color mode and a monochrome mode. These two modes are set by the user operating an operation panel (not shown). When the full color mode is set, the image forming apparatus shown in FIG. 2 has four toners corresponding to yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively. Using the image forming unit, each toner image forming unit forms a toner image of each color in synchronization with the feeding of the intermediate transfer belt, and superimposes the toner images on an intermediate transfer belt as an intermediate medium (primary Transfer), the toner image superimposed on the intermediate transfer belt is transferred (secondary transfer) to a sheet as a recording medium and fixed. On the other hand, when the monochrome mode is set, the image forming apparatus shown in FIG. 2 uses only the toner image forming unit corresponding to the black (K) toner among the four toner image forming units to generate a black toner image. Then, the black toner image is secondarily transferred onto a sheet through a primary transfer onto an intermediate transfer belt and fixed.

  As shown in FIG. 2, the image forming apparatus 100 is supported by four toner image forming units 110Y, 110M, 110C, and 110K, four primary transfer rolls 120, and a plurality of support rolls 131 in a counterclockwise direction. A semi-conductive intermediate transfer belt 130 that circulates in the direction, a secondary transfer device 140 that performs secondary transfer, and a fixing device 150 that fixes an unfixed toner image on a sheet.

  The four toner image forming units 110Y, 110M, 110C, and 110K are arranged side by side in the circulation direction of the intermediate transfer belt 130, and each toner image forming unit 110Y, 110M, 110C, and 110K rotates clockwise. A photosensitive drum 111 is provided. The surface of each photosensitive drum 111 is in contact with the surface of the intermediate transfer belt 130. The primary transfer roll 120 is disposed at a position facing the photosensitive drum 111 with the intermediate transfer belt 130 interposed therebetween, and a primary transfer region is formed between the photosensitive drum 111 and the primary transfer roll.

  Each of the toner image forming units 110Y, 110M, 110C, and 110K also includes a charger 112, a developing device 113, and a cleaning device 114. The developing device 113 is disposed on the upstream side of the primary transfer region around the photosensitive drum 111. The charger 112 is disposed further upstream than the developing unit 113. Further, the cleaning device 114 is disposed on the downstream side of the primary transfer region around the photosensitive drum 111.

  A charging bias in which an AC voltage is superimposed on a DC voltage is applied to the charger 112, and the surface of the photosensitive drum 111 is uniformly charged by the charger 112. The surface of the photosensitive drum 111 that is uniformly charged by the charger 112 is irradiated with laser light corresponding to image information from an exposure unit (not shown) to form an electrostatic latent image on the surface of the photosensitive drum 111. The developer 113 stores toner, and the toner is charged to a predetermined polarity in the developer. A developing bias in which an alternating voltage is superimposed on a direct current voltage is applied to the developing device 113, and the developing device 113 develops the electrostatic latent image formed on the surface of the photosensitive drum 111 with toner by the action of the developing bias. Then, a toner image is formed on the surface of the photosensitive drum 111. A primary transfer bias having a polarity opposite to the polarity of the toner is applied to the portion of the intermediate transfer belt 130 passing through the primary transfer region by the primary transfer roll 120. The toner image formed on the surface of the photosensitive drum 11 is transferred from the surface of the photosensitive drum to the surface of the intermediate transfer belt 130 by the action of the primary transfer bias.

  In the full color mode, each toner image forming unit 110Y, 110M, 110C, 110K is applied with a charging bias or a developing bias to form each color toner image, and each color toner image is superimposed on the intermediate transfer belt 130 as a single toner image. become. On the other hand, in the monochrome mode, the remaining three toner image forming units excluding the black toner image forming unit among the four toner image forming units are not applied with a charging bias or developing bias, and no toner image is formed. A black toner image is formed only by the toner image forming unit of toner, and the black toner image is carried on the intermediate transfer belt 130.

  The toner that is not transferred to the intermediate transfer belt 130 in the primary transfer region and remains on the photosensitive drum 111 is removed from the photosensitive drum 111 by the cleaning device 114.

  The secondary transfer device 140 includes a secondary transfer roll 141 arranged in pressure contact with the surface (toner image carrying surface) side of the intermediate transfer belt 130 and a backup roll 142 arranged on the back side of the intermediate transfer belt 130. The intermediate transfer belt 130 is sandwiched between these two rolls 141 and 142. A region sandwiched between these two rolls 141 and 142 becomes a secondary transfer region.

  In the full color mode, the sheet P is fed into the secondary transfer area in accordance with the timing at which the toner images overlapped on the intermediate transfer belt 130 reach the secondary transfer area. In the monochrome mode, the intermediate transfer belt 130 is fed. The paper P is fed into the secondary transfer area in accordance with the timing at which the black toner image carried on the toner reaches the secondary transfer area.

  Secondary transfer baice having the same polarity as the polarity of the toner is applied to the backup roll 142. The toner image on the intermediate transfer belt 30 is electrostatically repelled from the intermediate transfer belt 30 by the action of the secondary transfer bias and transferred onto the paper P. The sheet P that has passed through the secondary transfer device 140 is transported to the fixing device 150 by the transport belt 160. The fixing device 150 includes a heating roll 151 having a heating mechanism inside, and a fixing belt 152 pressed against the heating roll 151. The paper P that has passed through the secondary transfer region is sent between the heating roll 151 and the fixing belt 152. The toner constituting the toner image on the paper P is melted by the heating roll 151 and is fixed to the paper P by receiving pressure from the fixing belt 152 to form an image composed of the fixed toner image.

  A belt cleaner 170 that removes residual toner on the intermediate transfer belt 130 is provided on the downstream side of the secondary transfer device 140.

  Next, an AC superimposed bias generation circuit that generates a charging bias applied to the charging device 112 and a developing bias applied to the developing device 113 shown in FIG. 2 will be described. The image forming apparatus 100 shown in FIG. 2 includes two AC superimposed bias generation circuits having the same configuration. One AC superimposed bias generation circuit generates a charging bias, and the other AC superimposed bias generation circuit generates a developing bias. Is generated. Here, two AC superimposed bias generation circuits having the same configuration will be described as circuits that simply generate an AC superimposed bias without distinguishing between those that generate a charging bias and those that generate a development bias.

  FIG. 3 is a block diagram showing an AC superimposed bias generation circuit in the present embodiment.

  The AC superimposed bias generation circuit 180 shown in FIG. 3 is connected to the charger 112 or the developer 113 shown in FIG. 2, and the generation control of the AC superimposed bias applied thereto is controlled by yellow (Y) and magenta (M). , And cyan (C) and black (K). That is, the AC superimposed bias generation circuit 180 has DC high-voltage power supplies 181y, 181m, 181c, and 181k for generating a high DC voltage for each color, but has only one AC voltage power supply 182 for generating a basic AC voltage. However, the AC voltage generation circuit that transforms the AC voltage generated by the AC voltage power supply 182 to a desired voltage is common to the first generation circuit 183k dedicated to black and the three colors of yellow, magenta, and cyan. Only the second generation circuit 183ymc. The second generation circuit 183ymc common to the three colors connects the AC voltage of the AC superimposed bias for these three colors to the connection line 184 that electrically connects the AC voltage power supply 182 and the first generation circuit 183k dedicated to black. It is generated by transforming the applied applied AC voltage. In addition, a switching circuit 186 that switches whether or not the second generation circuit 183ymc generates an AC voltage is provided in the middle of the connection line 185 branched from the connection line 184 and connected to the second generation circuit 183ymc.

  In the AC superimposed bias generation circuit 180 shown in FIG. 3, the AC voltage generated by the first black generation circuit 183k is superimposed on the direct current voltage generated by the black dedicated high voltage power supply 181k, so that yellow, magenta, and cyan are generated. The AC voltage generated by the second generation circuit 183ymc common to these three colors is superimposed on the DC voltage generated by each of the DC high-voltage power supplies 181y, 181m, and 181c.

  FIG. 4 is a circuit diagram of the AC voltage bias generator, the switching circuit, the first generation circuit, and the second generation circuit extracted from the AC superimposed bias generation circuit shown in FIG.

  The first generation circuit 183k illustrated in FIG. 4 includes an operational amplifier 1831 and a transformer 1832. The negative terminal of the operational amplifier 1831 is connected to the AC voltage power supply 182 via a capacitor 1833 and a resistor 1834 connected in series. On the other hand, the plus terminal of the operational amplifier 1831 is connected to the reference power source 1835. The operational amplifier 1831 is provided with a negative feedback resistor 1836. Further, the output terminal of the operational amplifier 1831 is connected to the primary side coil of the transformer 1832 via the capacitor 1837. The AC voltage output from the output terminal of the operational amplifier 1831 is boosted by the transformer 1832, and the secondary side coil of the transformer 1832 outputs the AC voltage (AC-K) of the black-only AC superimposed bias. .

  In addition, a switch circuit 1861 as a switching circuit 186 is provided between the node A and the second generation circuit 183ymc in the connection line 184 that electrically connects the AC voltage power supply 182 and the first generation circuit 183k dedicated to black. . The switch circuit 1861 electrically connects the connection line 185 connecting the node A and the second generation circuit 183ymc by turning it on, and electrically cuts it by turning it off.

  The second generation circuit 183ymc shown in FIG. 4 is also the same as the circuit configuration of the first generation circuit 183k, and redundant description is omitted here, and the same elements are denoted by the same reference numerals used in the description of the first generation circuit 183k. To explain. In the second generation circuit 183ymc, the negative terminal of the operational amplifier 1831 is connected to one end of the switch circuit 1861 via a capacitor 1833 and a resistor 1834 (RC circuit) connected in series, and the negative terminal of the operational amplifier 1831 Is supplied with a signal (original signal) representing a voltage applied to the node A when the switch circuit 1861 is turned on. The AC voltage output from the output terminal of the operational amplifier 1831 is boosted by a transformer 1832 provided in the second generation circuit 183ymc, and the secondary coil of the transformer 1832 generates an AC of the AC superimposed bias common to the three colors. A voltage (AC-YMC) is output.

  Therefore, when the full color mode is set, the control unit (not shown) turns on the switch circuit 1861 so that the charger 112 and the developer 113 of all the toner image forming units 110Y, 110M, 110C, and 110K are turned on. When the AC superimposing bias is applied and the monochrome mode is set, the control unit switches off the switch circuit 1861 so that the charger 112 and the developer 113 of the toner image forming unit 110K that forms a black toner image are formed. The AC superposition bias is applied only to.

  Therefore, since the first generation unit 183k and the second generation unit 183ymc generate the AC voltage of the AC superimposed bias using the common AC voltage power source 182, the AC component is colored while reducing the mounting area of the substrate. As a result, the occurrence of problems relating to AC components such as voltage interference and insufficient insulation distance is prevented. Further, when the switch circuit 1861 is turned on / off in accordance with the mode switching between the full color mode and the monochrome mode, wasteful toner consumption can be suppressed and the life of the photosensitive drum 111 that is charged can be extended.

  Subsequently, four modified examples of the switching circuit 186 will be described. In the following description, overlapping description is omitted, and the same elements as those shown in FIG. In any of the four modifications, the switching circuit 186 includes a switch circuit, which is turned off by a control unit (not shown) when set to the full color mode and set to the monochrome mode. In some cases, it is turned on by the control unit.

  FIG. 5 is a circuit diagram showing an example in which the switching circuit of the first modification is used instead of the switching circuit shown in FIG.

  The switching circuit 186 illustrated in FIG. 5 includes an operational amplifier 1862, a switch circuit 1863, and a resistor 1864. The plus terminal of the operational amplifier 1862 arranged in the switching circuit 186 is connected to the node A, and the minus terminal is connected to the output terminal of the operational amplifier 1862. The operational amplifier 1862 of the switching circuit 186 is an amplifier that amplifies the AC voltage applied to the node A at an equal magnification. Note that a buffer may be used instead of the operational amplifier 1862. The output terminal of the operational amplifier 1862 having the same amplification factor is connected to a capacitor 1833 arranged on the input side of the second generation circuit 183ymc via a resistor 1864. In addition, a switch circuit 1863 is provided in a connection path 187 connecting the node B and the ground between the resistor 1864 and the capacitor 1833. When the switch circuit 1863 is turned on, the output of the operational amplifier 1862 having the same amplification factor is grounded.

  In the first modification, when the full color mode is set, a control unit (not shown) turns off the switch circuit 1863 so that a signal representing the AC voltage applied to the node A is output from the operational amplifier 1862 as it is. , Input to the second generation circuit 183ymc. Therefore, in the second generation circuit 183ymc, the AC voltage applied to the node A is transformed, and an AC voltage (AC-YMC) having a desired voltage value is used as the AC voltage of the AC superimposing bias for three colors. Generate. In addition, the first generation circuit 183k transforms the AC voltage applied to the node A, and generates an AC voltage (AC-K) having a desired voltage value as the AC voltage of the black-only AC superimposed bias. To do. On the other hand, when the control unit turns on the switch circuit 1863 due to the setting to the monochrome mode, the signal from the switching circuit 186 becomes the “L” level, and this “L” level signal is the operational amplifier 1831 of the second generation circuit 183ymc. Is input. As a result, no AC voltage (AC-YMC) is output from the second generation circuit 183ymc. Further, the voltage level of the node A hardly changes, and the first generation circuit 183k transforms the AC voltage applied to the node A, and a desired voltage as the AC voltage of the black-only AC superimposed bias. A value alternating voltage (AC-K) is generated.

  The AC superimposed bias generation circuit using the switching circuit of the first modification can be designed independent of the output capability of the AC voltage power supply 182.

  FIG. 6 is a circuit diagram showing an example in which the switching circuit of the second modified example is used instead of the switching circuit shown in FIG.

The switching circuit 186 shown in FIG. 6 includes a switch circuit 1863. This switch circuit 1863 is branched from a path 188 electrically connecting the operational amplifier 1831 and an RC circuit 183 _RC comprising a capacitor 1833 and a resistor 1834 connected in series to constitute the second generation circuit 183ymc. Yes, turning on turns the output of the RC circuit 183 _RC to ground.

  In the second modification, when the full color mode is set, the switch circuit 1863 is turned off, and both the first generation circuit 183k and the second generation circuit 183ymc transform the AC voltage applied to the node A. Thus, AC voltages (AC-K, AC-YMC) having desired voltage values are generated. On the other hand, when the monochrome mode is set, the switch circuit 1863 is turned on, a current flows from the node A to the switch circuit 1863, and the input to the negative terminal of the operational amplifier 1831 of the second generation circuit 183ymc becomes zero. As a result, the operational amplifier 1831 does not operate, and no AC voltage (AC-YMC) is output from the second generation circuit 183ymc. Further, the change in voltage level at the node A is suppressed by the capacitor 1833 of the second generation circuit 183ymc, and the first generation circuit 183k transforms the AC voltage generated by the AC voltage power supply 182 to a desired voltage (AC-K). To do.

  In the AC superimposed bias generation circuit using the switching circuit of the second modification, it is not necessary to use a so-called analog switch realized by an IC chip for the switch circuit 1863, and the switch circuit 1863 can be realized by a transistor. This is cost effective. In addition, since no operational amplifier is used in the switching circuit 186, it is advantageous in terms of cost.

  FIG. 7 is a circuit diagram showing an example in which the switching circuit of the third modification is used in place of the switching circuit shown in FIG.

FIG. 7 also shows an RC circuit 183 _RC comprising a capacitor 1833 and a resistor 1834 that are connected in series to constitute the second generation circuit 183ymc, as in FIG. In this RC circuit 183 _RC , a capacitor 1833 is provided on the input side, and a resistor 1834 connected in series to the capacitor 1833 is provided on the output side. The switching circuit 186 shown in FIG. 7 is branched from a path 189 electrically connecting the capacitor 1833 and the resistor 1834 of the RC circuit 183 _RC . The switching circuit 186 includes a switch circuit 1863 and a resistor 1866. The switch circuit 1863 is connected to a node C between the capacitor 1833 and the resistor 1834 via a resistor 1866, and the output of the capacitor 1833 constituting the RC circuit 183 _RC is turned on and grounded. The resistor 1866 is for suppressing the influence on the AC voltage power supply 182 due to the switch circuit 1863 being turned on.

  Also in the third modification, when the full color mode is set, the switch circuit 1863 is turned off, and both the first generation circuit 183k and the second generation circuit 183ymc transform the AC voltage applied to the node A. Thus, AC voltages (AC-K, AC-YMC) having desired voltage values are generated. On the other hand, when the monochrome mode is set, the switch circuit 1863 is turned on, and the input voltage to the negative terminal of the operational amplifier 1831 provided in the second generation circuit 183ymc is fixed in a DC manner. In this state, although the operational amplifier 1831 is operating, the output voltage of the operational amplifier 1831 is fixed in a DC manner near the maximum value, and no AC voltage (AC-YMC) is output from the second generation circuit 183ymc. Further, a change in voltage level at the node A is suppressed by the resistor 1866 provided in the switching circuit 186, and the first generation circuit 183k converts the AC voltage generated by the AC voltage power supply 182 to a desired voltage (AC-K). Transform.

  In the AC superimposed bias generation circuit using the switching circuit of the third modified example, the switch circuit 1863 can be realized by a transistor as in the second modified example, and an operational amplifier is not used for the switching circuit 186. Is advantageous.

  FIG. 8 is a circuit diagram showing an example in which the switching circuit of the fourth modified example is used instead of the switching circuit shown in FIG.

  The switching circuit 186 shown in FIG. 8 includes a switch circuit 1863. The switch circuit 1863 is a short circuit by turning on the negative feedback resistor 1836 of the operational amplifier 1831 provided in the second generation circuit 183ymc. Further, the operational amplifier 1831 of the second generation circuit 183ymc shown in FIG. 8 has a gain of zero when the negative feedback resistor 1836 is short-circuited.

  Also in the fourth modification, when the full color mode is set, the switch circuit 1863 is turned off, and both the first generation circuit 183k and the second generation circuit 183ymc transform the AC voltage applied to the node A. Thus, AC voltages (AC-K, AC-YMC) having desired voltage values are generated. On the other hand, when the monochrome mode is set, the switch circuit 1863 is turned on, the negative feedback resistor 1836 is short-circuited, and the operational amplifier 1831 provided in the second generation circuit 183ymc shown in FIG. The operational amplifier 1831 outputs a DC component but does not output an AC component, and no AC voltage (AC-YMC) is output from the second generation circuit 183ymc. In the first generation circuit 183k, the AC voltage applied to the node A is transformed, and an AC voltage (AC-K) having a desired voltage value is generated.

10 is a block diagram of a circuit for generating an AC superimposed bias disclosed in Patent Document 1. FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the AC superimposition bias generation circuit in this embodiment. FIG. 4 is a circuit diagram illustrating a portion of an AC voltage power supply, a switching circuit, a first generation circuit, and a second generation circuit extracted from the AC superimposed bias generation circuit illustrated in FIG. 3. FIG. 5 is a circuit diagram showing an example in which a switching circuit of a first modification is used instead of the switching circuit shown in FIG. 4. FIG. 5 is a circuit diagram showing an example in which a switching circuit of a second modification is used instead of the switching circuit shown in FIG. 4. FIG. 6 is a circuit diagram showing an example in which a switching circuit of a third modification is used instead of the switching circuit shown in FIG. 4. It is a circuit diagram which shows the example which replaced with the switching circuit shown in FIG. 4, and used the switching circuit of the 4th modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 110Y, 110M, 110C, 110K Toner image forming unit 111 Photoconductor drum 112 Charger 113 Developing device 120 Primary transfer roll 130 Intermediate transfer belt 140 Secondary transfer device 150 Fixing device 180 AC superimposing bias generation circuit 181y, 181m, 181c, 181k DC high voltage power supply 182 AC voltage power supply 183k first generation circuit 183ymc second generation circuit 1831 operational amplifier 1832 transformer 1833 capacitor 1833 resistance 183 _RC RC circuit 1836 negative feedback resistance 184, 185 connection line 186 switching circuit 1861 switch circuit 1862 Operational amplifier 1863 Switch circuit 1864 Resistor 1866 Resistor

Claims (7)

A plurality of toner image forming units are provided that form an electrostatic latent image on the image carrier by charging and exposure and develop the electrostatic latent image with toner to form a toner image on the image carrier. Transferring the toner images onto the recording medium so that the toner images formed by the toner image forming unit finally overlap each other on the recording medium, and fixing the transferred toner images onto the recording medium; In an image forming apparatus for forming an image composed of a fixed toner image on the recording medium by
Each of the plurality of toner image forming units includes an applied member to which an AC superimposed bias in which an AC voltage is superimposed on a DC voltage is applied,
This image forming apparatus further includes
An AC voltage generator for generating AC voltage;
An AC voltage generated by the AC voltage generator is used to generate an AC voltage of the AC superimposed bias to be applied to a member to be applied to a predetermined one or a plurality of toner image forming units among the plurality of toner image forming units. A first generator that generates voltage by transforming;
A member to be applied provided in one or more predetermined toner image forming units among the remaining toner image forming units excluding the predetermined one or more toner image forming units from the plurality of toner image forming units. The second generation is generated by transforming the AC voltage of the AC superimposed bias applied to the AC voltage applied to the connection line that electrically connects the AC voltage generator and the first generator. And
Possess a switching portion that switches whether to generate an alternating voltage to the second generating unit,
When the switching unit is turned on with an amplifier that is provided in the middle of a path that branches from the connection line and is electrically connected to the second generation unit, and that amplifies the signal of the applied AC voltage at an equal magnification An image forming apparatus comprising: a switch circuit for grounding an output of the amplifier to ground .   2. The image forming apparatus according to claim 1, wherein the member to be applied is a charger that applies the AC superimposed bias and charges the image carrier by the action of the AC superimposed bias.   The developing device for developing the electrostatic latent image formed on the image bearing member with toner by the action of the AC superimposed bias, wherein the AC superimposed bias is applied to the member to be applied. The image forming apparatus according to 1.   The switching unit is a switch circuit that is provided in the middle of a path that branches from the connection line and is electrically connected to the second generation unit, and shuts off the electrical connection of the path by turning off. The image forming apparatus according to claim 1, wherein: The second generation unit includes an RC circuit including a capacitor and a resistor connected in series, and an operational amplifier to which an output of the RC circuit is input, and boosts an output from the operational amplifier.
  The image forming apparatus according to claim 1, wherein the switching unit includes a switch circuit that, when turned on, grounds an output of the RC circuit to a ground.   The second generation unit includes an RC circuit in which a capacitor is provided on the input side and a resistor connected in series with the capacitor is provided on the output side, and an operational amplifier to which an output of the RC circuit is input. Boosts the output from
  The switching unit includes a switch circuit that, when turned on, grounds the output of the capacitor of the RC circuit to ground, and when the switch circuit is turned on, the output of the operational amplifier is fixed in a DC manner. The image forming apparatus according to claim 1.   The second generation unit includes an operational amplifier that has a negative feedback resistor and the amplification factor becomes zero when the resistor is short-circuited, and boosts the output from the operational amplifier.
  The image forming apparatus according to claim 1, wherein the switching unit includes a switch circuit that short-circuits the resistor when turned on.

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