JP2015004836A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to form an excellent image on various recording materials different in volume resistance value, without increasing cost or body size.SOLUTION: An apparatus for supplying a current to a transfer nip part Nt via a guide member 17 and a recording material P during transfer operation includes: a common transfer voltage power source 18 which applies a voltage to a transfer roller 5 for transfer operation and applies a voltage to the guide member 17; a variable resistor 19b which is arranged on an electric path between the transfer voltage power source 18 and the guide member 17, and changes electrical resistance according to an environment where the image forming apparatus is used; and a varistor 20 connected in parallel with the guide member 17 between the guide member 17 and the variable resistor 19b in the electric path.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet.

In an image forming apparatus (image recording apparatus) using an image forming process such as an electrophotographic system or an electrostatic recording system, an image is formed on a recording material such as paper as follows. First, an electrostatic latent image is formed on a photosensitive drum, the latent image is developed using a developer and visualized as a toner image, and the toner image is transferred to a transfer nip portion formed between the photosensitive drum and a transfer roller. Transfer onto the recording material. Thereafter, the recording material onto which the toner image has been transferred is nipped and conveyed by a nip formed between a fixing roller and a pressure roller provided in the fixing device, whereby the toner image is heat-fixed on the recording material. In this way, an image is formed on the recording material.
In such an image forming apparatus, in order to stably convey the recording material to the transfer nip portion, a guide member for guiding the recording material to be conveyed is disposed upstream of the transfer nip portion in the recording material conveyance direction. There is. A part of the guide member is made of a conductive material to prevent electrification due to rubbing against the recording material. By being grounded, image defects and toner scattering due to overcharging of the guide member are prevented. Yes.
The recording material has various electrical volume resistance values. It absorbs moisture under high-temperature and high-humidity environment, etc., and thin paper with low volume resistance value or dried under low-temperature and low-humidity environment etc. It is various.
The constant current control is preferable for the transfer control for uniformly applying charges to recording materials having different volume resistance values.
However, for recording materials with low volume resistance, such as moisture-absorbing paper, the transfer current escapes to the main body of the guide member and fixing device through the recording material, making it difficult to control with constant current control. Voltage control is often performed. However, even if constant voltage control is performed, there is a concern that an image defect may occur due to insufficient transfer current because countermeasures against escape of the transfer current to the main body are insufficient.
Although it is conceivable to set a high transfer output voltage for the above-mentioned problem, when a constant voltage control is performed with a uniquely determined transfer voltage, the resulting transfer current largely depends on the resistance of the recording material. For this reason, there is a concern that appropriate transfer to the recording material cannot be performed.
That is, if the transfer voltage is set to be high in consideration of the current escape of the recording material having a low volume resistance value, there is a concern that an image defect due to an excessive transfer current may occur in the recording material having a high volume resistance value. Further, when the transfer voltage is set such that no image defect occurs in a recording material having a high volume resistance value, there is a concern that an image defect due to insufficient transfer current occurs in a recording material having a low volume resistance value.

In order to solve the above-mentioned problem, Patent Document 1 proposes a configuration in which a voltage having the same polarity as the transfer voltage is applied to the guide member 117 as shown in FIG.
Here, FIG. 10A shows a state in which the recording material P is nipped and conveyed at the transfer nip portion Nt between the photosensitive drum 101 and the transfer roller 105 while being guided by the guide member 117. . Voltage is supplied to the transfer roller 105 and the guide member 117 from the power supply units 118a and 118b, respectively. The transfer current It is supplied to the transfer nip portion Nt by the electric field E formed by the power supply portions 118a and 118b. FIG. 10B is a diagram showing the configuration shown in FIG. 10A with an equivalent circuit, where Rp is the resistance of the recording material P, and Rr is the resistance of the transfer roller 5.
With such a configuration, when there is a transfer current escape to the main body through a recording material having a low volume resistivity such as a moisture absorbent paper, it is possible to compensate for the transfer current escape, so an image due to a shortage of the transfer current Defects can be prevented. Further, since a current from the guide member 117 hardly flows through a recording material having a high volume resistance value, it is possible to prevent an excessive transfer current from being obtained, and a good image can be obtained with various recording materials having different volume resistance values. Can be obtained.

JP-A-7-239617

However, in the above configuration, since it is necessary to provide a power supply separately from the transfer voltage power supply, there is a concern that the cost increases and the size of the main body increases.
The present invention has been made in view of the above-described circumstances, and forms better images on various recording materials having different volume resistance values without incurring an increase in cost or an increase in the size of the main body. An object of the present invention is to provide an image forming apparatus that can perform the above-described process.

In order to achieve the above object, the present invention provides:
An image carrier on which a toner image is formed;
A transfer member that performs a transfer operation of forming a transfer nip portion with the image carrier and transferring a toner image on the image carrier to a recording material at the transfer nip portion;
A guide member for guiding the recording material to be conveyed toward the transfer nip portion;
In an image forming apparatus having
For the transfer operation, a common power supply unit that applies a voltage to the transfer member and a voltage to the transfer member;
A resistance unit provided in an electrical path between the power source unit and the guide member, the resistance unit having a magnitude of electrical resistance that varies depending on a use environment of the image forming apparatus;
A voltage stabilizing element connected in parallel to the guide member between the guide member and the resistance portion of the electrical path;
It is characterized by providing.

  According to the present invention, there is provided an image forming apparatus capable of forming a better image on various recording materials having different volume resistance values without causing an increase in cost and an increase in body size. Is possible.

Sectional drawing which shows schematic structure of the image forming apparatus which concerns on embodiment The figure shown about the transfer voltage application structure in Example 1. FIG. Diagram showing transfer voltage application configuration in the study example The figure which shows the structure which has arrange | positioned the varistor in parallel with the guide member of the examination example Diagram showing the relationship between the breakdown voltage of varistors and image defects The figure which shows the relationship between control and image defect when a fixed resistance is passed in parallel with the guide member The figure which shows the relationship between the possibility of control by the temperature and humidity of the atmosphere of Example 1, and an image defect. The figure shown about the transfer voltage application structure in Example 2. FIG. The figure shown about the transfer voltage application structure in Example 3. FIG. FIG. 3 is a diagram illustrating a transfer voltage application configuration of a conventional image forming apparatus.

DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to the present embodiment. FIG. 1 shows a laser beam printer as an example of the image forming apparatus.
First, the configuration of the image forming apparatus shown in FIG. 1 will be described.
The image forming apparatus includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is configured by providing a photosensitive material such as OPC (organic optical semiconductor), amorphous selenium, or amorphous silicon on a cylindrical drum base formed of aluminum, nickel, or the like. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in the direction of the arrow Rd by the driving source m1.

Around the photosensitive drum 1, a charging device (charging roller) 2, an exposure unit 3, a developing device 4, a transfer roller 5 as a transfer member, and a cleaning device 6 are arranged in order along the rotation direction.
In addition, a feeding cassette 7 that stores a recording material P such as paper is disposed below the apparatus main body M. A feeding roller 8, a conveyance roller 9, a top sensor 10, a conveyance guide 11, a fixing device 12, a discharge sensor 13, a conveyance roller 14, a discharge roller 15, and a discharge tray 16 are sequentially arranged along the conveyance path of the recording material P. Has been placed.

Next, the operation of the image forming apparatus will be described.
The photosensitive drum 1 that is rotationally driven in the direction of the arrow Rd by the drive source m1 is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 2. The photosensitive drum 1 after charging is subjected to image exposure L based on the image information by the exposure means 3 such as a laser optical system on the surface, and the charge of the exposed portion is removed to form an electrostatic latent image (latent image). Is done. The electrostatic latent image is developed (visualized) by the developing device 4. The developing device 4 includes a developing roller 4a. A developing bias is applied to the developing roller 4a, and toner (developer) is attached to the electrostatic latent image on the photosensitive drum 1, whereby the toner is placed on the photosensitive drum 1. An image is formed.
The toner image on the photosensitive drum 1 is transferred to the recording material P by the transfer roller 5. The transfer roller 5 is pressed against the photosensitive drum 1 by a transfer pressure spring (not shown) so as to be driven and rotated by the photosensitive drum 1. Further, with this configuration, a transfer nip portion Nt is formed between the transfer roller 5 and the photosensitive drum 1. As described above, the transfer roller 5 performs a transfer operation for transferring the toner image on the photosensitive drum 1 (on the image carrier) onto the recording material P at the transfer nip portion Nt.

The recording material P is stored in the feeding cassette 7, fed one by one by the feeding roller 8, then conveyed by the conveying roller 9, and guided by the guide member 17 through the top sensor 10. It is conveyed to the transfer nip portion Nt.
At this time, the leading edge of the recording material P is detected by the top sensor 10 and synchronized with the toner image on the photosensitive drum 1.
During the transfer operation, a transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied to the transfer roller 5 from a transfer voltage power supply 18 serving as a power supply unit, whereby the toner image on the photosensitive drum 1 is transferred to the recording material P. Transferred to a predetermined position above.
The recording material P carrying the transferred unfixed toner image on the surface is transported to the fixing device 12 along the transport guide 11, where the unfixed toner image is heated and pressed, thereby the surface of the recording material P The toner image is fixed to the toner image.

The fixing device 12 is a pressure roller driving type fixing device using a flexible endless belt as a fixing film. The fixing device 12 mainly includes a fixing film 12a, a pressure roller 12b in contact with the fixing film 12a, a ceramic heater (hereinafter referred to as a heater) 12c for heating toner through the fixing film 12a, and a heater holder 12d. It is configured as a member.
The pressure roller 12b is provided with a heat-resistant elastic layer having elasticity such as silicone rubber on the outer peripheral surface of a metal core, and a material having high releasability such as fluororesin is used for the outermost layer. A release layer is provided. The pressure roller 12b presses the fixing film 12a against the heater 12c from below by the outer peripheral surface of the release layer with a pressure spring (not shown) to form a fixing nip portion Nf between the pressure roller 12b and the fixing film 12a.

The pressure roller 12b is rotationally driven in the direction of the arrow R12b by the driving source m1, so that a rotational force acts on the fixing film 12a by the pressure frictional force of the fixing nip portion Nf. Thereby, the fixing film 12a is driven to rotate in the direction of the arrow R12a while the inner surface thereof is in close contact with the downward surface of the heater 12c and slides.
In the fixing operation, the pressure roller 12b is rotationally driven, and accordingly the fixing film 12a is driven and rotated, power is supplied to the heater 12c, and the heater 12c is heated to rise to a predetermined temperature and adjusted in temperature. It is done in the state.
In such a state, the recording material P carrying the unfixed toner image is introduced between the fixing film 12a and the pressure roller 12b in the fixing nip portion Nf. In the fixing nip portion Nf, the recording material P is nipped and conveyed together with the fixing film 12a in a state where the toner image carrying surface side is in close contact with the outer peripheral surface of the fixing film 12a.
In this nipping and conveying process, the heat of the heater 12c is applied to the recording material P through the fixing film 12a, and the unfixed toner image on the recording material P is heated and pressurized to be melted and fixed on the recording material P. The recording material P that has passed through the fixing nip portion Nf is separated from the fixing film 12a by curvature.

The recording material P on which the toner image is fixed is transported by the transport roller 14 and discharged onto the discharge tray 16 on the upper surface of the apparatus main body by the discharge roller 15.
On the other hand, after the toner image is transferred, the toner (transfer residual toner) that has not been transferred to the recording material P and remains on the drum surface is removed by the cleaning blade 6a of the cleaning device 6 and used for the next image formation. .
By repeating the above operation, image formation can be performed one after another.

[Examination example]
FIG. 3A is a diagram showing a transfer voltage application configuration in the study example, and FIG. 3B is a diagram showing the configuration shown in FIG. 3A with an equivalent circuit. Here, in FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1 for convenience of explanation.
As described above, when a power source for applying a voltage to the guide member 17 is provided separately from the transfer voltage power source 18, there is a concern that the cost may be increased and the size of the main body may be increased.
In order to solve this problem, a configuration as shown in FIG. 3A in which an electric path from the transfer voltage power supply 18 is branched and a transfer voltage is applied to the guide member 17 is conceivable. That is, the transfer voltage power supply 18 is a common power supply unit that applies a voltage to the transfer roller 5 and a voltage to the guide member 17 for the transfer operation. Here, in FIG. 3, Rp is the volume resistance value (hereinafter simply referred to as resistance) of the recording material P, Rc is the resistance of the fixed resistor 19 a, and Rr is the resistance of the transfer roller 5.

The recording material P conveyed toward the transfer nip Nt while being guided by the guide member 17 is in contact with both the photosensitive drum 1 and the transfer roller 5 at the transfer nip Nt.
Here, a transfer current It is supplied to the transfer nip portion Nt by an electric field E formed by the transfer voltage power source 18, and an output from the transfer voltage power source 18 is controlled by a transfer voltage control unit (hereinafter, control unit) 21. . The current I supplied from the transfer voltage power source 18 flows to the current I ₂ supplied to the transfer nip portion Nt via the transfer roller 5 and the fixed resistor 19a, and is transferred via the guide member 17 and the recording material P. The path is divided into a path of current I ₁ supplied to the nip portion Nt and contributing to transfer. In this way, the transfer voltage power supply 1 that supplies current to the transfer nip portion Nt via the transfer roller 5.
8, the current can be supplied to the transfer nip portion Nt via the guide member 17 and the recording material P.

It is applied to the guide member 17 in accordance with the transfer output voltage that varies depending on the temperature and humidity of the environment in which the image forming apparatus is used (hereinafter referred to as ambient temperature and humidity), the resistance Rr of the transfer roller, the resistance Rp of the recording material P, and the like. The voltage also fluctuates. Therefore, the configuration shown in FIG. 3, when the voltage output from the transfer voltage power supply 18 is high, the more the transfer current I ₄ applied from the guide member 17, an image defect (strength loss due to current contributing excessive to transfer (Image) may occur.
Therefore, a voltage stabilizing element such as a varistor or a Zener diode having a nonlinear resistance characteristic is connected in parallel with the guide member 17 so that the voltage applied to the guide member 17 is kept below a certain level (predetermined below). It is possible to suppress the occurrence of strong missing images.

FIG. 4 is a view showing a configuration in which the varistor 20 is arranged in parallel with the guide member 17.
As the resistance Rc of the fixed resistor 19a arranged in series with the guide member 17, a resistor having a resistance value of 1 × 10 ⁸ Ω was used. Here, the fixed resistor 19a disposed between the transfer voltage power supply 18 and the guide member 17 is disposed for the purpose of preventing the current flowing through the varistor 20 from being excessive and causing failure.

The potential of the guide member 17, to change the breakdown voltage of the varistor 20, the breakdown voltage is low, the even lower potential of the guide member 17, causes a current I ₄ is reduced, the effect is insufficient to compensate for the transfer current shortage . On the other hand, when the breakdown voltage is high and the potential of the guide member 17 is also high, the current I ₄ becomes excessive, and a strong dropout image may be generated due to excessive transfer current. Therefore, the breakdown voltage of the varistor 20 needs to be adjusted. Become.

In the configuration of FIG. 4, the relationship between the possibility of constant current control and the image defect when the resistance value of the fixed resistor 19a is changed under a 15 ° C./10% environment as a low temperature and low humidity environment was examined. The examination result at this time is shown in FIG. Further, in the configuration of FIG. 4, the relationship between the possibility of constant voltage control and the image defect when the resistance value of the fixed resistor 19a is changed in a 30 ° C./80% environment as a high temperature and high humidity environment was examined. The examination result at this time is shown in FIG. Here, the control unit 21 performs constant current control and constant voltage control using a varistor having a breakdown voltage of 200 V and a fixed resistor having two resistance values of 1 × 10 ⁸ Ω and 5 × 10 ¹¹ Ω. Each went. As the recording material, Canon A4 size paper Extra 80 (basis weight 80 g / m ² ) was used.

When the resistance value of the fixed resistor 19a is 1 × 10 ⁸ Ω, it is difficult to execute the constant current control because the current I ₃ flowing through the GND through the varistor varies depending on the varying transfer bias. It is.
On the other hand, when the resistance value of the fixed resistor 19 a is 5 × 10 ¹¹ Ω, the current I ₁ through the fixed resistor 19 a does not flow, and the voltage output from the transfer voltage power supply 18 is The current I ₁ did not flow even if the output range was 0 to 6 kV or less. For this reason, constant current control was possible, and no image defect occurred.

Further, in a high temperature and high humidity environment (30 ° C./80%), the resistance value of the fixed resistor 19a connected in series with the guide member 17 is 1 × 10 ⁸ Ω or 5 × 10 ¹¹ Ω. Even so, constant voltage control is possible. However, when the resistance value of the fixed resistor 19a is 5 × 10 ¹¹ Ω, the current I ₁ through the fixed resistor 19a does not flow, and the voltage applied to the guide member 17 is low. An image defect occurred. On the other hand, when the resistance value of the fixed resistor 19a was 1 × 10 ⁸ Ω, no image defect occurred.
As described above, the resistance value of the resistor arranged in series with the guide member 17 is preferably low resistance in a high temperature and high humidity environment and high resistance in a low temperature and low humidity environment, and the electric resistance varies depending on the temperature and humidity of the atmosphere. I found out that it was necessary.

Therefore, in this embodiment, the voltage stabilizing element is arranged in parallel with the guide member 17, and the resistance value of the resistance unit arranged in series with the guide member 17 is low resistance in a high temperature and high humidity environment, and low temperature and low humidity environment. Below, it is characterized by having a high resistance configuration. Here, the resistance portion may be provided in the electrical path between the transfer voltage power supply 18 and the guide member 17 and the magnitude of the electrical resistance may be changed according to the use environment of the image forming apparatus. That is, the resistance portion may be configured so that the electrical resistance can be set smaller in an environment where the temperature is high and high humidity than in an environment where the temperature and humidity is low.
An embodiment to which such a characteristic configuration is applied will be described below. Here, in each Example, the same code | symbol is attached | subjected about the component similar to embodiment mentioned above, and the description is abbreviate | omitted. The image forming apparatus shown in FIG. 1 is provided with temperature / humidity detection means 31 for detecting the temperature / humidity of the atmosphere.

[Example 1]
FIG. 2A is a diagram showing a transfer voltage application configuration in Example 1, and FIG. 2B is a diagram showing the configuration shown in FIG. 2A with an equivalent circuit.
In this embodiment, as shown in FIG. 2A, the varistor 20 is disposed in parallel with the guide member 17 as a voltage stabilizing element, and the variable resistor 19b is disposed in series with the guide member 17 as a resistance portion. It is characterized by that. Here, Rv shown in FIG. 2B is the resistance of the variable resistor 19b. The variable resistor 19b can change the magnitude of electrical resistance in accordance with the temperature and humidity of the atmosphere.
Current I supplied from the transfer voltage power source 18, the current I ₂ supplied to the transfer nip portion Nt via a transfer roller 5, divided into the path of the current I ₁ flowing through the variable resistor 19b side. Further, the current I ₁ is divided into a current I ₃ that flows to GND via the varistor 20 and a current I ₄ that flows to the transfer nip portion Nt via the guide member 17 and the recording material P.

In this example, first, a suitable application range of the breakdown voltage of the varistor 20 was obtained using a paper phenol substrate as a variable resistor in a high temperature and high humidity environment (30 ° C./80%).
FIG. 5 is a diagram showing the relationship between the breakdown voltage of the varistor and image defects.
In this example, as shown in FIG. 5, the investigation was performed using varistors having breakdown voltages of 50V, 100V, 200V, 300V, 400V, and 500V. At that time, a transfer voltage of about 1 kV is output from the transfer voltage power supply 18.
When the breakdown voltage of the varistor 20 is 100 V or less as a result of outputting an image under such conditions, the potential of the guide member 17 does not rise above 100 V, and the current supplied from the guide member 17 to the recording material P is insufficient. Therefore, there was a concern about the occurrence of image defects. On the other hand, in a varistor having a breakdown voltage of 400 V or more, there is a concern about the occurrence of image defects due to excessive current.
Therefore, the varistor 20 used in the present embodiment is preferably one having a breakdown voltage of 200V to 300V.

FIG. 7 is a diagram showing the relationship between the possibility of control by the temperature and humidity of the atmosphere and the image defect in the configuration of FIG.
Here, a varistor having a breakdown voltage of 200V is used, and the temperature and humidity detection means 31 is used to perform constant voltage control of the transfer output voltage of 1 kV in an environment of 30 ° C./80%, and in an environment of 15 ° C./10%. Constant current control of 10 μA was performed. The resistance Rv of the variable resistor 19b varies depending on the temperature and humidity of the atmosphere, and is an insulator in a low temperature and low humidity environment, but becomes 1 × 10 ⁸ Ω in a high temperature and high humidity environment.

When a constant current control of 10 μA is performed by the controller 21 in an environment of 15 ° C./10%, the current I ₂ flowing through the transfer roller 5 is 10 μA, and the variable resistor 19b is almost an insulator. current _{I 1} flowing through the body 19b becomes 0 .mu.A. In this case, the current I ₃ flowing to the GND via the varistor 20 does not flow even if the voltage output from the transfer voltage power supply 18 fluctuates between 0 to 6 kV or less which is the output range of the transfer voltage power supply 18. Therefore, constant current control is possible and there is no image defect.
On the other hand, in the environment of 30 ° C./80%, the value of the resistance Rv of the variable resistor 19b decreases to 1 × 10 ⁹ and when the controller 21 performs constant voltage control of 1 kV, the guide member 17 Since the transfer current flows, there is no image defect and the result is OK.

As described above, in this embodiment, the transfer voltage power supply 18 is a common power supply unit that applies a voltage to the transfer roller 5 and a voltage to the guide member 17 for the transfer operation. As a result, it is possible to provide an image forming apparatus capable of forming a better image on various recording materials having different volume resistance values without causing an increase in cost and an increase in the size of the main body. Become. In the present embodiment, in order to realize this power supply unit, the variable resistor 19 b as a resistance unit is arranged in series with the guide member 17, and the varistor 20 is arranged in parallel with the guide member 17. By adopting such a configuration, constant current control is possible in a low temperature and low humidity environment, and constant voltage control is possible in a high temperature and high humidity environment while preventing image defects due to insufficient transfer current.
Therefore, it is possible to obtain a better image while enabling suitable transfer control regardless of the temperature and humidity of the atmosphere.

  Here, in this embodiment, the paper phenol substrate is used as the variable resistor, but the present invention is not limited to this. That is, as the variable resistor, any material that changes its electric resistance depending on the temperature and humidity of the atmosphere, such as ion conductive material, nylon, other polyester resin, phenol resin, acrylic resin, polypropylene resin, paper, etc., is suitably applied. It is possible.

[Example 2]
Example 2 will be described below. FIG. 8A is a diagram showing a transfer voltage application configuration in this embodiment, and FIG. 8B is a diagram showing the configuration shown in FIG. 8A with an equivalent circuit.
As the resistance portion arranged in series with the guide member 17, the variable resistor 19 b is applied in the above-described first embodiment. However, in this embodiment, two or more resistance values are used as shown in FIG. The resistor is used, and the resistor is switched by switching.
That is, in this embodiment, the resistance value is low fixed resistor R ₁ of 1 × 10 ⁸ _Ω, and the two resistors of the high fixed resistance 5 × 10 ¹¹ Ω resistor R _2, switch them A switching element 22 as a switch is arranged in series with the guide member 17.
In this embodiment, the switching element 22 is switched to the low fixed resistor R ₁ in a high temperature and high humidity environment and to the high fixed resistor R ₂ in a low temperature and low humidity environment.

Here, the switching operation by the switching element 22 is preferably operated by the control means based on the detection result of the temperature / humidity detection means 31. That is, when the detection result by the temperature / humidity detection means 31 is high temperature and high humidity, the control means can switch the fixed resistor so that the magnitude of the electric resistance of the resistance portion is smaller than that in the case of low temperature and low humidity. It is good to be controlled by.
Further, the switching operation by the switching element 22 may be accompanied by a user selection operation. For example, the switching operation of the resistor by the switching element 22 may be performed by the user selecting a mode corresponding to the temperature and humidity of the atmosphere based on the detection result by the temperature and humidity detection means 31. Even if the temperature / humidity detecting means 31 is not provided in the image forming apparatus, the switching operation of the resistor by the switching element 22 is performed by the user selecting a mode corresponding to the temperature / humidity of the atmosphere. It is good to be.
In the present embodiment, the configuration in which the two types of resistors are switched by the switching element 22 has been described, but the present invention is not limited to this. By switching to any one of the plurality of fixed resistors each having a resistance value corresponding to the temperature and humidity of the atmosphere by the switching element 22, the guide member from the transfer voltage power supply 18 through the fixed resistor What is necessary is just to form the electrical path connected to 17.

  With such a configuration, it is possible to obtain the same effect as that described in the first embodiment. Here, in the first embodiment, the resistance value of the variable resistor 19b continuously changes depending on a change in the environment, whereas in the second embodiment, the resistance value of the resistor is a fixed value, and thus the switching is performed. The control unit 21 can execute more accurate control according to the resistance value.

[Example 3]
Example 3 will be described below. FIG. 9A is a diagram showing a transfer voltage application configuration in this embodiment, and FIG. 9B is a diagram showing the configuration shown in FIG. 9A with an equivalent circuit.
As a resistor arranged in series with the guide member 17, a fixed resistor 19a is used in this embodiment as shown in FIG. 9A, and a switch for switching ON / OFF of the electric path in series with the fixed resistor 19a. The switching element 23 is arranged. As described above, the switching element 23 is configured to be able to switch the electrical path connected from the transfer voltage power supply 18 to the guide member 17 via the fixed resistor 19a between the connection state (ON) and the cutoff state (OFF). ing.
In this embodiment, the switching element 23 is switched to OFF in a low temperature and low humidity environment and to ON in a high temperature and high humidity environment.
Here, the switching operation of the switching element 23 may be operated by the control unit based on the detection result of the temperature / humidity detection unit 31 as in the second embodiment, or may be accompanied by the user's selection operation. There may be.

With such a configuration, it is possible to obtain the same effect as that described in the first embodiment. Further, with the construction of this embodiment, since it is possible to interrupt the current I ₁ through the fixed resistor 19a in a low-temperature and low-humidity environment, the constant current control of the control unit 21, the more accurately feasible.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 5 ... Transfer roller, 17 ... Guide member, 18 ... Transfer voltage power supply, 19b ... Variable resistor, 20 ... Varistor, Nt ... Transfer nip part, P ... Recording material

Claims (8)

An image carrier on which a toner image is formed;
A transfer member that performs a transfer operation of forming a transfer nip portion with the image carrier and transferring a toner image on the image carrier to a recording material at the transfer nip portion;
A guide member for guiding the recording material to be conveyed toward the transfer nip portion;
In an image forming apparatus having
For the transfer operation, a common power supply unit that applies a voltage to the transfer member and a voltage to the transfer member;
A resistance unit provided in an electrical path between the power source unit and the guide member, the resistance unit having a magnitude of electrical resistance that varies depending on a use environment of the image forming apparatus;
A voltage stabilizing element connected in parallel to the guide member between the guide member and the resistance portion of the electrical path;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the power supply unit is controlled at a constant current in an environment where the use environment is low temperature and humidity, and is controlled at a constant voltage in an environment where the environment is high temperature and humidity.   3. The image forming apparatus according to claim 1, wherein the resistance portion is provided with a variable resistor capable of changing a magnitude of electric resistance corresponding to temperature and humidity of the use environment. In the resistance portion,
A plurality of fixed resistors each having a resistance value corresponding to the temperature and humidity of the use environment;
A switch that switches to any one of the plurality of fixed resistors and forms the electrical path from the power supply unit to the guide member via the fixed resistors;
The image forming apparatus according to claim 1, wherein an image forming apparatus is provided. Temperature / humidity detection means for detecting the temperature and humidity of the use environment,
When the detection result by the temperature and humidity detection means is high temperature and high humidity, the switch has a smaller electric resistance of the fixed resistor that forms the electric path than the case of low temperature and low humidity. The image forming apparatus according to claim 4, wherein the fixed resistor can be switched. In the resistance portion,
A fixed resistor;
A switch that can be switched between a connected state and a cut-off state of the electrical path connected to the guide member from the power supply unit via the fixed resistor;
The image forming apparatus according to claim 1, wherein an image forming apparatus is provided. Temperature / humidity detection means for detecting the temperature and humidity of the use environment,
The switch sets the electrical path to a cut-off state when the detection result by the temperature and humidity detection means is low temperature and low humidity, and sets the electrical path to a connected state when the detection result is high temperature and high humidity. The image forming apparatus according to claim 6.   The image forming apparatus according to claim 1, wherein the voltage stabilizing element is a varistor or a Zener diode.

Images