JPH0540426A - Fixing device self-bias impressing circuit - Google Patents

Abstract

PURPOSE:To prevent a diode from being destroyed by an overcurrent in the case of the maintenance and the inspection, etc., of a fixing device by connecting a resistance element to a rectifying element in series. CONSTITUTION:A heating roller 1 has a halogen heater inside and is made of aluminum, and the surface thereof is coated in an insulated state. A spring 2 which contacts by two points is disposed at the end part of the roller 1, and a carbon resistance 3 of about 100kOMEGA and the diode 4 being the rectifying element, whose reverse breakdown strength is about 600V-2kV, are connected to the spring 2 in series, then the anode side of the diode 4 is grounded. A pressure roller 5 having high-resistance conductive sponge on the core bar of a center part is disposed under the roller 1 so that it may press-contact with the roller 1, and a contact 6 is connected to the end part of the core bar of the roller 5. A carbon resistance 7 of about 100kOMEGA and the same diode 8 as the diode 4 are connected to the contact 6 in series and the cathode side of the diode 8 is grounded. Therefore, a current is restricted by the resistance 7, so that the diode is prevented from being destroyed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for applying a self-bias to a roller in an electrophotographic recording apparatus using a heat roller fixing device.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic apparatus using a heat roller fixing device, in order to prevent toner as a developer on a recording medium (paper) from being offset to a heating roller, a potential having the same polarity as the toner is applied to the roller. In some cases, a structure in which the roller and the toner repel each other is used. In order to apply a potential to the roller, there are a method in which a voltage is applied to the roller from a power source and a method in which frictional charging due to rubbing between the recording medium and the roller is used. In particular, the method using triboelectrification is also called a self-bias method, and is widely used for a simple configuration in which a diode as a rectifying element is inserted between the roller and the ground. When a reverse voltage is applied to this diode, a breakdown occurs when the reverse breakdown voltage is exceeded, and the diode exhibits a constant voltage characteristic. When the roller thus configured and the recording medium rub against each other, the roller is charged, the electric charge in the forward direction flows to the ground, and the electric charge in the reverse direction is accumulated in the roller. Since the breakdown of the diode occurs as described above when a certain amount of charge is accumulated, the potential of the roller is kept constant. As a result, the toner receives an electrostatic repulsive force from the roller, and the offset is prevented.

[0003]

However, in the above-mentioned conventional example, when the fixing device unit is replaced by a service person or a user, there is a possibility that the end portion of the diode or the roller may be touched. At this time, if a human being is charged, an excessive current may flow in the diode, which may destroy the diode.

The electrostatic breakdown of the diode is caused by an excessive current. For example, when the internal resistance of the diode is 1 KΩ,
A discharge of a human body charged to 25 KV causes a peak current of 25 A to flow. However, since the diode used for self-bias is a small diode having a reverse withstand voltage of 1 KV and a current of several hundreds mA, the junction is destroyed when a peak current of 25 A flows.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a fixing device self-bias applying circuit capable of preventing overcurrent breakdown of a diode at the time of maintenance and inspection of the fixing device.

[0006]

According to the present invention, the above object is achieved by connecting a rectifying element whose one end is grounded to a core metal of a heating roller and a pressure roller arranged in pressure contact with each other. This is achieved by connecting a resistance element in series to the rectifying element in a fixing device self-bias applying circuit that applies a bias voltage in the direction of pulling away from the heating roller side to the pressing roller side.

[0007]

According to the present invention, when a person is charged during maintenance and inspection of the fixing device, a large current tends to flow through the rectifying element when the roller or the end of the rectifying element is touched. Since a resistance element is connected in series with the element, the current is limited. Therefore, overcurrent breakdown of the rectifying element is prevented.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment and a second embodiment of the present invention will be described with reference to the drawings.

<First Embodiment> In FIG. 1, 1 is a heating roller of a fixing device. The heating roller 1 is an aluminum roller having a halogen heater therein, and the surface thereof is insulation-coated. A spring 2 is provided at the end of the heating roller 1 and is in contact with the heating roller 1 at two points. The spring 2 has a carbon resistance 3 of about 100 KΩ and a reverse withstand voltage of 600 V.
A diode 4, which is a rectifying device of about 2 KV, is connected in series, and the anode side of the diode 4 is grounded. On the other hand, below the heating roller 1, a pressure roller 5 having a conductive sponge of high resistance is disposed so as to be in pressure contact with a cored bar at the center, and the end of the cored bar of the pressure roller 5 is arranged. A contact 6 is connected to the section. A carbon resistor 7 of about 100 KΩ and a diode 8 similar to the diode 4 are connected in series to the contact 6, and the cathode side of the diode 8 is grounded.

In the apparatus of this embodiment as described above, when the paper on which the toner is placed passes between the heating roller 1 and the pressure roller 5, the toner is melted and fixed. At this time, the rollers 1 and 5 are charged due to the friction between the paper and the rollers 1 and 5. The electric charges that flow a current in the forward direction of the diodes 4 and 8 immediately escape to the ground, but the charges that flow a current in the reverse direction are blocked by the diodes and remain on the roller.

In the connection of FIG. 1, the heating roller 1 is positively charged,
A negative charge remains on the pressure roller 5. If the toner on the paper has a positive charge, it receives a repulsive force from the heating roller 1 and a suction force on the pressure roller 5, so that the toner is heated by the heating roller 1.
No longer offset to.

In the structure shown in FIG. 1, the core metal of the heating roller 1 and the pressure roller 5 may be touched by a service person or a user when the fixing unit is replaced. At this time, if the resistors 3 and 7 are not present, a large current flows through the diode to the ground when the person is charged, and the diode is destroyed. However, in the device of this embodiment, the current is limited by connecting a resistor of about 100 KΩ, so that the diode is prevented from being destroyed.

The carbon resistors are used as the resistors 3 and 7 because the carbon resistors are strong against the rush current. As a result of the experiment, the resistance value of the metal film resistance changed after one discharge.

FIG. 2 shows a method of actually mounting resistors and diodes. The resistor 3 and the diode 4 are connected in series, and the connection portion is pressure-bonded by the closed end connector 9. Soldering may be used, but crimping is better in terms of workability.

A round terminal 10 is crimped to one end of the diode 4, and a round terminal 11 is crimped to one end of the resistor 3. Round terminal 1
0 is fixed to the frame with a screw, and the round terminal 11 is fixed to the spring 2 with a screw.

The resistor 3 and the diode 4 are linearly arranged. If the round terminal 11 is close to the lead wire of the diode 4, the current does not pass through the resistor 3 when static electricity is applied. This is because the round terminal 11 is discharged to the diode 4. When there is such a possibility, it is effective to cover the insulating tube as shown by the dotted line 12 to secure the creepage distance and prevent the discharge.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

This embodiment is different from the first embodiment in that the number of resistors connected to the diodes 3 and 8 is one. As shown in FIG. 3, a resistor 13 is connected to the ground side of the diodes 3 and 8 and grounded. By connecting in this way, the number of resistors can be reduced.

Although the fixing device of the heat roller fixing type has been described in the above embodiments, the present invention has the same effect when used in the fixing device of the pressure fixing type.

[0020]

As described above, according to the present invention,
By connecting a resistor of about 100 KΩ in series to the self-biasing diode, the current during electrostatic discharge can be limited to a sufficiently small value, and overcurrent breakdown of the diode can be prevented.

During normal operation, the current flowing through the diode is about 1 μA, the voltage drop due to the resistance of 100 KΩ is about 0.1 V, and the bias voltage is 600 V to 2K.
The value is sufficiently small with respect to V, and there is no problem in preventing offset.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a method of mounting a rectifying element and a resistance element in the apparatus shown in FIG.

FIG. 3 is a diagram showing a schematic configuration of a second embodiment device of the present invention.

[Explanation of symbols]

 1 Heating roller 3,7 Resistance element (carbon resistance) 4,8 Rectifying element (diode) 5 Pressure roller

Claims (1)

[Claims] 1. A direction in which a rectifying element whose one end is grounded is connected to a core metal of a heating roller and a pressure roller which are arranged in pressure contact with each other, and a developer is pulled away from the heating roller side and pulled to the pressure roller side. In the fixing device self-bias applying circuit for applying the bias voltage of, the fixing device self-bias applying circuit is characterized in that a resistance element is connected in series to the rectifying element.