Patent Application
20250138456
This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2023-186071 filed on Oct. 31, 2023, the entire contents of which are incorporated herein by reference.
The present disclosure relates to an image forming apparatus including a fixing device.
An electrophotographic image forming apparatus includes a transfer device and a fixing device. The transfer device transfers a toner image onto a sheet. The fixing device applies heat and pressure to the toner image on the sheet to fix the toner image to the sheet.
The fixing device may include a planar heater having a substrate and a plurality of resistors formed on the substrate.
An image forming apparatus according to one aspect of the present disclosure includes a transfer device, a fixing device, and a control device. The transfer device transfers a toner image onto a sheet. The fixing device applies heat and pressure to the toner image on the sheet. The control device controls the fixing device. The fixing device includes a heater, a holding member, a fixing member, a pressure roller, a drive mechanism, and a resistance measuring circuit. The holding member includes a metal portion and holds the heater. The fixing member is a flexible cylindrical fixing member having an inner peripheral surface in contact with the heater. The pressure roller is rotatably supported, and applies pressure to the toner image on the sheet by sandwiching the fixing member and the sheet between the pressure roller and the heater. The drive mechanism rotates the pressure roller. The resistance measuring circuit measures electrical resistance of the metal portion of the holding member. The control device controls whether to allow or prohibit a supply of power to the heater in accordance with a rotation state of the pressure roller and a measured resistance value of the resistance measuring circuit.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.
Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. Note that the following embodiment is merely an example of a technique according to the present disclosure, and does not limit the technical scope of the technique according to the present disclosure.
As shown in
The printing device 4 executes a printing process for forming an image on a sheet 9. The printing device 4 executes the printing process by an electrophotographic method. The sheet 9 is an image forming medium such as paper or a sheet-like resin member.
The sheet conveying device 3 includes a sheet feeding device 30 and a plurality of sets of conveying roller pairs 31. The sheet feeding device 30 feeds out the sheet 9 stored in the sheet storing portion 2 to a conveying path 300 in the main portion 1. The conveying path 300 forms a passage through which the sheet 9 is conveyed.
The plurality of sets of conveying roller pairs 31 are rotationally driven by a motor (not shown). The plurality of sets of conveying roller pairs 31 rotate to convey the sheet 9 along the conveying path 300, and then discharge the sheet 9 into a discharge tray 1x.
The sheet 9 passes through a transfer position P1 and a fixing position P2 on the conveying path 300, and is discharged into the discharge tray 1x.
In the following description, a sheet conveying direction along the conveying path 300 is referred to as a conveying direction D01. The fixing position P2 is a position downstream of the transfer position P1 in the conveying direction D01.
In addition, a direction crossing the conveying direction D01 in the conveying path 300 is referred to as a main direction D1. In the present embodiment, the main direction D1 is a direction perpendicular to the conveying direction D01. The main direction D1 is the main scanning direction in the printing process.
The printing device 4 forms a toner image on a sheet 9 conveyed along the conveying path 300. The toner image is a developer image using toner as a developer. The toner is an example of a granular developer.
The printing device 4 includes one or more image forming portions 4x, a laser scanning unit 40, a transfer device 44, and a fixing device 5. The image forming portion 4x includes a drum-shaped photoconductor 41, a charging device 42, a developing device 43, a drum cleaning device 45, and the like.
The image forming apparatus 10 shown in
In the image forming portion 4x, the photoconductor 41 rotates, and the charging device 42 charges the surface of the photoconductor 41. Furthermore, the laser scanning unit 40 writes an electrostatic latent image on the surface of the photoconductor 41 by scanning with a laser beam.
Moreover, the developing device 43, by supplying the toner to the surface of the photoconductor 41, develops the electrostatic latent image into the toner image. The photoconductor 41 is an example of an image-carrying member that rotates while carrying the toner image.
The transfer device 44 transfers the toner image onto the sheet 9 at a transfer position P1 on the conveying path 300. The transfer device 44 includes an intermediate transfer belt 441, four primary transfer devices 442 corresponding to the four image forming portions 4x, a secondary transfer device 443, and a belt cleaning device 444.
In the transfer device 44, the primary transfer device 442 transfers the toner image on the surface of the photoconductor 41 onto the surface of the intermediate transfer belt 441. Thus, a color toner image is formed on the surface of the intermediate transfer belt 441.
The secondary transfer device 443 transfers the toner image formed on the intermediate transfer belt 441 onto the sheet 9 on the conveying path 300.
Note that in a case in which the image forming apparatus 10 is a monochrome image forming apparatus, the secondary transfer device 443 transfers the toner image on the photoconductor 41 onto the sheet 9 on the conveying path 300.
The drum cleaning device 45 removes waste toner remaining on the surface of the photoconductor 41. The belt cleaning device 444 removes the waste toner remaining on the intermediate transfer belt 441.
The fixing device 5 heats and presses the toner image on the sheet 9 while conveying the sheet 9 at a fixing position P2 on the conveying path 300. As a result, the fixing device 5 fixes the toner image on the sheet 9 to the sheet 9.
As shown in
The pressure roller 51, the fixing member 52, the holding member 54, and the heater 53 are each arranged along the main direction D1 at the fixing position P2. The pressure roller 51, the fixing member 52, the heater 53 and the holding member 54 are formed to extend in the main direction D1.
The fixing member 52 is a flexible cylindrical member. For example, the fixing member 52 is a cylindrical film member. The fixing member 52 is rotatably supported by a holding member 54. The inner peripheral surface of the fixing member 52 comes in contact with the heater 53.
The pressure roller 51 is rotatably supported. The pressure roller 51, by coming into pressure contact with the fixing member 52, forms a nip Np1 between the pressure roller 51 and the fixing member 52 (see
When the sheet 9 passes through the fixing position P2, the pressure roller 51 pressurizes the toner image on the sheet 9 by sandwiching the fixing member 52 and the sheet 9 between the pressure roller 51 and the heater 53. The heater 53 heats the toner image on the sheet 9 via the fixing member 52.
The drive mechanism 50 rotates the pressure roller 51. For example, the drive mechanism 50 includes a motor and a gear mechanism.
As the pressure roller 51 rotates, the fixing member 52 rotates in conjunction with the pressure roller 51. As the fixing member 52 rotates, the inner circumferential surface of the fixing member 52 slides on the surface of the heater 53. An inner peripheral surface of the fixing member 52 is coated with a lubricant.
The holding member 54 holds the heater 53 and rotatably supports the fixing member 52. The heater 53 is held by the holding member 54 in a state aligned with the main direction D1. The holding member 54 has a synthetic resin portion 54a and a metal portion 54b.
The synthetic resin portion 54a holds the heater 53. The synthetic resin portion 54a is arranged facing the pressure roller 51 with the fixing member 52 interposed therebetween. The metal portion 54b holds the synthetic resin portion 54a. For example, the metal portion 54b is made of a metal such as iron or stainless steel.
The biasing mechanism 56 elastically biases the metal portion 54b of the holding member 54 toward the pressure roller 51. That is, the biasing mechanism 56 elastically biases the fixing member 52 toward the pressure roller 51 via the holding member 54.
The temperature sensor 55 detects the temperature of the heater 53. The temperature detected by the temperature sensor 55 is used to control the fixing temperature. The fixing temperature control is a feedback control in which the power supplied to the heater 53 is controlled by comparing the temperature detected by the temperature sensor 55 with a preset target temperature.
The control device 8 executes various types of data processing, and controls devices such as the sheet conveying device 3 and the printing device 4. The objects to be controlled by the control device 8 include conveying of the sheet 9 by the sheet conveying device 3 and power supply to the heater 53 of the fixing device 5.
As shown in
Furthermore, the control device 8 includes a communication device 85 and a power supply circuit 86.
The CPU 81 is a processor that executes various types of data processing and control by executing computer programs.
The RAM 82 is a computer-readable volatile storage device. The RAM 82 temporarily stores the computer programs executed by the CPU 81 and data output and referenced by the CPU 81 in the course of executing various types of processes.
The CPU 81 includes a plurality of processing modules that are achieved by executing the computer programs. The plurality of processing modules include a main control portion 8a, a heater control portion 8b, and a printing control portion 8c.
The main control portion 8a executes control such as start control for starting various types of processes in response to an operation on an operation device (not shown).
The heater control portion 8b controls the amount of power supplied to the heater 53 by controlling the fixing temperature. The heater control portion 8b adjusts the amount of power supplied to the heater 53 by controlling the power supply circuit 86.
The power supply circuit 86 supplies power to the heater 53 in accordance with a power supply command from the heater control portion 8b.
The printing control portion 8c controls the sheet conveying device 3. Furthermore, the printing control portion 8c causes the printing device 4 to execute the printing process in synchronization with the conveying of the sheet 9 by the sheet conveying device 3.
The control device 8 controls the power supply to the heater 53 and controls the sheet conveying device 3 through the actions of a heater control portion 8b and a printing control portion 8c, and further controls the image forming portion 4x and the transfer device 44.
The secondary storage device 83 is a computer-readable non-volatile storage device. For example, one or both of a flash memory and a hard disk drive may be employed as the secondary storage device 83.
The signal I/F 84 converts detection signals output by various types of sensors into digital data, and transmits the digital data to the CPU 81. Furthermore, the signal I/F 84 converts the control command output by the CPU 81 into a control signal, and transmits the control signal to the object to be controlled.
The communication device 85 executes communication with other devices such as a host device that transmits a printing job to the image forming apparatus 10. The CPU 81 communicates with the other devices through the communication device 85.
In the present embodiment, the heater 53 is a planar heater having a plurality of resistors 6 (see
The heater 53 includes a substrate 6x, a plurality of resistors 6, one or more power supply electrodes 600, and a ground electrode 610 (see
The substrate 6x is a non-conductive member. For example, the substrate 6x is a film. A plurality of resistors 6 are formed on the surface of a substrate 6x. Each resistor 6 is a heating element that generates heat when power is supplied thereto.
In the present embodiment, the plurality of resistors 6 are divided into a plurality of resistor blocks 61. Each of the plurality of heater blocks 60 includes a plurality of resistors 6 arranged in the main direction D1.
The heater 53 includes a plurality of power supply electrodes 600 corresponding to a plurality of resistor blocks 61 (see
In each drawing, a sub-direction D2 is a direction along the conveying direction D01. The sub-direction D2 is a direction crossing the main direction D1. The main direction D1 is the longitudinal direction of the heater 53. The sub-direction D2 is the widthwise direction of the heater 53.
The plurality of power supply electrodes 600 are electrically connected to first ends of the plurality of heater blocks 60 in the secondary direction D2. The ground electrode 610 is connected to second ends of the plurality of heater blocks 60 in the secondary direction D2. That is, the plurality of power supply electrodes 600 and the ground electrode 610 are electrically connected to the plurality of resistors 6.
The protective layer 62 is a non-conductive member that covers the plurality of resistors 6 and the plurality of electrodes 600 and 610 (see
The power supply circuit 86 is capable of supplying power individually to each heater block 60 via part of or all of the plurality of power supply electrodes 600 and the ground electrode 610.
The heater control portion 8b selects a target heater block from the plurality of heater blocks 60 in accordance with the size of the sheet 9 to be conveyed, and supplies power to the target heater block via the power supply circuit 86.
The plurality of resistors 6 in the heater 53 are arranged at slight intervals on the substrate 6x, and are thus electrically insulated. However, dielectric breakdown may occur in part of the resistors 6.
When the supply of power to the heater 53 continues when the dielectric breakdown occurs in a part of the heater 53, the entire heater 53 may become abnormally hot, and there is a possibility that a dangerous situation may occur.
Therefore, when localized dielectric breakdown occurs in the heater 53, it is desirable to be able to detect the occurrence of the dielectric breakdown as soon as possible and to stop the power supply to the heater 53.
The image forming apparatus 10 includes a configuration for quickly stopping the power supply to the heater 53 when the dielectric breakdown occurs in a part of the heater 53 in the fixing device 5. The configuration will be described below.
In the present embodiment, the fixing device 5 further includes a resistance measuring circuit 57 that measures electrical resistance of the metal portion 54b of the holding member 54 (see
For example, the resistance measuring circuit 57 includes one or more resistive elements that form a voltage divider circuit together with the metal portion 54b, a power source that supplies a minute current to the voltage divider circuit, and a voltage detection circuit that detects the voltage of the voltage divider circuit. In this case, the detected voltage of the voltage detection circuit represents the electrical resistance of the metal portion 54b.
The substrate 6x and the protective layer 62 have a relatively low heat transfer rate and low thermal conductivity. Therefore, in a case in which a part of the heater 53 becomes locally hot, the temperature may not be promptly reflected by the temperature sensor 55.
On the other hand, the metal portion 54b of the holding member 54 has a higher heat transfer rate and a higher thermal conductivity than the substrate 6x and the protective layer 62. Therefore, when a part of the heater 53 becomes hot, the temperature of the metal portion 54b increases quickly.
Furthermore, as the temperature of the metal portion 54b increases, electrical resistance of the metal portion 54b increases. That is, the electrical resistance of the metal portion 54b represents the temperature of the metal portion 54b.
In the following description, the resistance value of the metal portion 54b measured by the resistance measuring circuit 57 is referred to as a measured resistance value. The heater control portion 8b of the control device 8 controls whether to allow or prohibit the supply of power to the heater 53 in accordance with the rotation state of the pressure roller 51 and the resistance measurement value.
For example, the heater control portion 8b determines the rotation state of the pressure roller 51 according to the control state of the drive mechanism 50 by the print control portion 8c.
In the present embodiment, the heater control portion 8b controls whether to allow or prohibit the supply of power to the heater 53 in accordance with the magnitude relationship between the measured resistance value and a first reference value while the pressure roller 51 is stopped.
More specifically, the heater control portion 8b allows power supply to the heater 53 in a case in which the measured resistance value is lower than the first reference value while the pressure roller 51 is stopped. On the other hand, the heater control portion 8b prohibits the supply of power to the heater 53 in a case in which the measured resistance value exceeds the first reference value while the pressure roller 51 is rotating.
In addition, the heater control portion 8b controls whether to allow or prohibit the supply of power to the heater 53 in accordance with the magnitude relationship between the measured resistance value and a second reference value while the pressure roller 51 is rotating.
The amount of heat transferred from the heater 53 to the pressure roller 51 via the fixing member 52 is greater when the pressure roller 51 is rotating than when the pressure roller 51 is stopped.
Therefore, the temperature of the metal portion 54b when part of the heater 53 has risen to a predetermined upper limit temperature is lower when the pressure roller 51 is rotating than when the pressure roller 51 is stopped.
The first reference value corresponds to the electrical resistance of the metal portion 54b when a part of the heater 53 rises to the upper limit temperature while the pressure roller 51 is stopped. On the other hand, the second reference value corresponds to the electrical resistance of the metal portion 54b when a part of the heater 53 rises to the upper limit temperature while the pressure roller 51 is rotating.
Thus, the second reference value represents a greater resistance value than the first reference value. The first reference value and the second reference value are experimentally determined in advance.
Prohibiting the supply of power to the heater 53 includes stopping the supply of power to the heater 53 when power is being supplied to the heater 53, and not starting the supply of power to the heater 53.
Allowing the supply of power to the heater 53 includes allowing the supply of power to the heater 53 to continue when power is being supplied to the heater 53, and allowing the supply of power to the heater 53 to begin.
By employing the image forming apparatus 10, the supply of power to the heater 53 can be stopped immediately when the dielectric breakdown occurs in a part of the heater 53 in the fixing device 5. As a result, a dangerous situation is avoided.
It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-186071 | Oct 2023 | JP | national |
