JP2018124390A - Image forming apparatus and fixing control method - Google Patents

Abstract

An image quality of a printed image can be prevented from being lowered while avoiding damage to a driving force transmission mechanism. A control unit 3 of an image forming apparatus 1 operates a fixing motor 49 to drive a heating belt 53 while heating a lubricating grease by a heater 51 to reduce the viscosity, and a torque detection signal S1 is a torque. The driving speed of the fixing motor 49 is switched to a higher speed every time it falls below the reference signal S2. As a result, the image forming apparatus 1 can sufficiently suppress the torque generated in the fixing motor 49 while gradually heating each part of the heating belt 53, and thus can effectively reduce the occurrence of uneven gloss in the fixing process. At the same time, damage to the transmission mechanism that transmits the driving force from the fixing motor 49 to the pressure roller 55 of the fixing unit 21 can be reduced. [Selection] Figure 9

Description

  The present invention relates to an image forming apparatus and a fixing control method, and is suitable for application to, for example, an electrophotographic printer.

  2. Description of the Related Art Conventionally, as an image forming apparatus, for example, an exposure apparatus generates a toner image based on image data and transfers it to a sheet, and then the image is printed by fixing the sheet by applying heat or pressure to the sheet by a fixing unit. is there.

  The fixing unit includes, for example, a belt formed in a cylindrical shape, a heating unit that contacts and heats the inner peripheral surface of the belt, and a driving force transmitted to the belt via a transmission mechanism. Some have a drive section that travels along the direction. Further, in this fixing unit, lubrication grease is applied to the inner peripheral surface of the belt, so that the friction between the belt and the heating unit may be reduced to run smoothly.

  Such a lubricating grease has heat resistance and a characteristic that the viscosity decreases at a high temperature, considering that it is heated in the heating section, but the viscosity increases at a low temperature, for example, at a normal temperature. For this reason, in the fixing unit to which the grease is applied, when the driving of the belt is started by the driving unit at room temperature (that is, in a state where the temperature is relatively low), the driving unit and the transmission mechanism may be damaged.

  Therefore, in the image forming apparatus, when the operation of the fixing unit is started, the heating unit heats the belt while the belt is stopped, and accordingly, the temperature of the grease is also increased to reduce the viscosity, thereby performing control called preheating. The thing is proposed (for example, refer patent document 1).

Japanese Patent No. 5744737 (FIGS. 8 and 9, etc.)

  However, in the image forming apparatus having such a configuration, heating is performed while the belt is stopped by preheating in the fixing unit, and therefore, a state where a locally high temperature occurs in the belt, that is, temperature unevenness in the circumferential direction occurs. It occurs. When the toner image is fixed on the paper by the fixing unit in such a state, the image forming apparatus may cause deterioration in image quality in the printed image, such as uneven gloss on the image fixed on the paper. There was a problem.

  The present invention has been made in consideration of the above points, and intends to propose an image forming apparatus and a fixing control method capable of preventing deterioration in image quality of a printed image while avoiding damage to a driving force transmission mechanism. Is.

  In order to solve such a problem, in the image forming apparatus of the present invention, an image forming unit that forms a developer image representing an image with a developer, and an endless inner surface coated with a lubricant and run in the circumferential direction. A fixing unit for contacting the outer peripheral surface of the belt to a medium having a developer image transferred thereon, and a heating unit that locally contacts and heats the inner peripheral surface of the belt A driving unit that transmits driving force to the vehicle, a torque detection unit that detects torque of the driving unit, and a control unit that controls the driving unit based on a torque detection result by the torque detection unit, In the initial driving process in which the heating unit is heated and the belt is driven by the driving unit, the driving speed by the driving unit is changed according to the torque detection result of the torque detecting unit.

  In the fixing control method of the present invention, in the predetermined fixing portion, the belt is formed by a heating portion that is endless and has a lubricant applied to the inner peripheral surface and abuts on the inner peripheral surface of the belt that can travel in the circumferential direction. A heating step for locally heating the belt, a driving step for driving the belt by transmitting a driving force from a predetermined driving unit, a detecting step for detecting the torque of the driving unit by a predetermined torque detecting unit, a predetermined step, A control step for controlling the drive speed by the drive unit according to the torque detection result detected in the detection step by the control unit, and an image for forming a developer image in which the image is expressed by the developer by the predetermined image forming unit A forming step and a fixing step for bringing the belt into contact with the medium onto which the developer image has been transferred are provided in the fixing unit.

  In the present invention, the belt can be run while the belt is heated by the heating unit, and after the torque becomes an appropriate torque to be changed, the driving unit can change the driving speed to the next driving speed. Accordingly, the present invention can gradually heat the belt part by part while avoiding an excessive torque being applied to the transmission mechanism.

  According to the present invention, it is possible to realize an image forming apparatus and a fixing control method capable of preventing deterioration in image quality of a printed image while avoiding damage to a driving force transmission mechanism.

1 is a schematic diagram illustrating a configuration of an image forming apparatus. It is a basic diagram which shows the structure of an image forming unit. 1 is a block diagram illustrating a circuit configuration of an image forming apparatus. It is a basic diagram which shows the structure of a fixing part and a torque detection part. It is an approximate line figure showing change of temperature and torque with progress of time. It is a basic diagram which shows the relationship of the tradeoff in preheat temperature and initial stage drive speed. It is a flowchart which shows a preheating process procedure. It is a flowchart which shows an initial drive process sequence. It is an approximate line figure showing change of torque, temperature, and drive speed with progress of time.

  Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[1. Configuration of image forming apparatus]
As shown in FIG. 1, the image forming apparatus 1 is a so-called printer, and can print a desired color image on a sheet P having a size such as A3 size or A4 size.

  In the image forming apparatus 1, various components are arranged inside a printer housing 2 formed in a substantially box shape. In the following description, the right end portion in FIG. 1 is defined as the front surface of the image forming apparatus 1, and the vertical direction, the horizontal direction, and the front-rear direction when viewed from the front are defined and described.

  The image forming apparatus 1 is configured to perform overall control by the control unit 3. The control unit 3 is connected to a host device (not shown) such as a computer device wirelessly or by wire. The control unit 3 executes print processing for forming a print image on the surface of the paper P when image data representing an image to be printed is given from the host device and printing of the image data is instructed.

  A paper feed tray 4 that accommodates the paper P is provided at the bottom of the printer housing 2. A paper feed unit 5 is provided in front of and above the paper feed tray 4. The paper feed unit 5 is opposed to each other with the pickup roller 6 disposed on the front upper side of the paper feed tray 4, the transport guide 7 that guides the paper P forward and backward or upward along the transport path U, and the transport path U. A pair of paper feed rollers 8, a pair of registration rollers 9, and a pair of transport rollers 10. The paper feeding unit 5 is provided with a registration sensor 11 that detects the presence or absence of the paper P immediately below the registration roller pair 9, and a writing sensor 12 that detects the presence or absence of the paper P immediately after the conveyance roller pair 10. Is provided.

  The paper feed unit 5 picks up and conveys the paper P stored in the paper tray 4 while being separated one by one by appropriately rotating each roller based on the control of the control unit 3. The guide 7 is advanced forward and upward along the conveyance path U, and finally comes into contact with the registration roller pair 9. The registration roller pair 9 is appropriately prevented from rotating, and by applying a frictional force to the paper P, the so-called skewing in which the side of the paper P is inclined with respect to the traveling direction is corrected. It is made to advance after the state where the edge of is aligned along the left and right. Subsequently, the paper feeding unit 5 advances the paper P rearward and upward along the conveyance path U, and finally delivers it to the middle conveyance unit 13 disposed behind the writing sensor 12.

  The middle conveyance unit 13 has a configuration in which a transfer belt 16 formed of an endless belt is stretched around a transfer belt driving roller 14 disposed on the front side and a rear roller 15 disposed on the rear side. When the driving force is transmitted to the transfer belt drive roller 14 from a motor described later, the intermediate conveyance unit 13 causes the transfer belt 16 to travel by appropriately rotating the roller 15 thereafter. As a result, the transfer belt 16 travels the upper portion along the conveyance path U, that is, the portion stretched between the transfer belt driving roller 14 and the rear roller 15 in the backward direction. At this time, when the paper P is delivered from the paper feeding unit 5, the middle transport unit 13 moves the paper P backward as the transfer belt 16 travels with the paper P placed on the upper side of the transfer belt 16. Make it progress.

  Four image forming units 17C, 17M, 17Y and 17K are arranged in order from the rear side to the front side on the upper side of the middle conveyance unit 13 and on the opposite side of the middle conveyance unit 13 across the conveyance path U. ing. Image forming units 17C, 17M, 17Y, and 17K (hereinafter collectively referred to as image forming unit 17) correspond to cyan (C), magenta (M), yellow (Y), and black (K), respectively. However, only the colors are different, and both are configured similarly.

  As shown in the schematic side view of FIG. 2, the image forming unit 17 includes an image forming unit 31, a toner cartridge 32, and a print head 33, and the transfer roller 18 disposed below the image forming unit 31. The transfer belt 16 is sandwiched between the two. Incidentally, the image forming unit 17 and each component constituting the image forming unit 17 have a sufficient length in the left-right direction according to the length in the left-right direction of the paper P. For this reason, many parts are relatively long in the left-right direction with respect to the length in the front-rear direction and the up-down direction, and are formed in an elongated shape along the left-right direction.

  The toner cartridge 32 contains toner as a developer, is disposed above the image forming unit 31, and is attached above the image forming unit 31. The toner cartridge 32 supplies the stored toner to the toner storage unit 34 of the image forming unit 31. In addition to the toner accommodating portion 34, the image forming portion 31 incorporates a supply roller 35, a developing roller 36, a regulating blade 37, a photosensitive drum 38, and a charging roller 39.

  The supply roller 35, the developing roller 36, the photosensitive drum 38, and the charging roller 39 are all formed in a columnar shape with the central axis extending in the left-right direction, and can be charged. ing. The regulating blade 37 is made of, for example, a stainless steel plate having a predetermined thickness, and a part thereof is brought into contact with the peripheral side surface of the developing roller 36 in a slightly elastically deformed state.

  The image forming unit 31 is supplied with a driving force from a motor (not shown) to rotate the supply roller 35, the developing roller 36, and the charging roller 39 in the direction indicated by the arrow R2 (counterclockwise in the drawing), and the photosensitive member. The drum 38 is rotated in the direction of arrow R1 (clockwise in the figure). Further, the image forming unit 31 applies a predetermined bias voltage to the supply roller 35, the developing roller 36, the regulating blade 37, and the charging roller 39 to charge each of them.

  The supply roller 35 attaches the toner in the toner accommodating portion 34 to the peripheral side surface by charging, and causes the toner to adhere to the peripheral side surface of the developing roller 36 by rotation. The developing roller 36 abuts the peripheral side surface against the peripheral side surface of the photosensitive drum 38 after excess toner is removed from the peripheral side surface by the regulating blade 37. At this time, the toner adhering to the peripheral side surface of the developing roller 36 is charged to a negative potential.

  On the other hand, the charging roller 39 is in contact with the photosensitive drum 38 in a charged state, thereby uniformly charging the peripheral side surface of the photosensitive drum 38 negatively. In the print head 33, light emitting elements made up of a large number of LEDs (Light Emitting Diodes) are linearly arranged along the left-right direction which is the main scanning direction. The print head 33 emits light with a light emission pattern based on an image data signal supplied from the control unit 3 (FIG. 1) (details will be described later), thereby exposing the photosensitive drum 38 and emitting light. Only raise the potential. Thereby, an electrostatic latent image is formed on the peripheral side surface of the photosensitive drum 38 in the vicinity of the upper end thereof.

  Subsequently, the photosensitive drum 38 is rotated in the direction of the arrow R <b> 1 to bring the portion where the electrostatic latent image is formed into contact with the developing roller 36. As a result, toner adheres to the peripheral side surface of the photosensitive drum 38 based on the electrostatic latent image, and the toner image based on the image data is developed.

  The transfer roller 18 is located directly below the photosensitive drum 38, and the upper portion of the transfer belt 16 is sandwiched between the vicinity of the upper end of the peripheral side surface and the vicinity of the lower end of the photosensitive drum 38. A predetermined bias voltage is applied to the transfer roller 18 and the transfer roller 18 is rotated in the direction of the arrow R2 by the transfer belt 16. As a result, when the paper P is being transported along the transport path U, the image forming unit 17 can transfer the toner image developed on the peripheral side surface of the photosensitive drum 38 onto the paper P.

  In this manner, each image forming unit 17 advances backward while sequentially transferring and superimposing the toner images of the respective colors on the paper P conveyed from the front along the conveyance path U.

  A cleaning blade 19 disposed below the rear roller 15 in the middle conveyance unit 13 (FIG. 1) is disposed at a position in contact with the transfer belt 16 to scrape off toner adhering to the transfer belt 16, and the cleaning blade 19 A waste toner box 20 is provided to store the toner scraped off by the above.

  A fixing unit 21 is provided near the rear end of the middle conveyance unit 13. When the paper P on which the toner image has been transferred is conveyed along the conveyance path U, the fixing unit 21 fixes the toner image by applying heat and pressure to the paper P, and sends the toner image backward (in detail). Will be described later).

  A paper discharge unit 22 is disposed behind the fixing unit 21. The paper discharge unit 22 has a configuration similar to that of the paper supply unit 5, and a conveyance guide 23 that guides the paper P, a conveyance roller pair 24, a discharge roller pair 25, a discharge sensor 26, and the like along the conveyance path U. Has been placed. The paper discharge unit 22 rotates the respective conveyance roller pairs appropriately according to the control of the control unit 3 so that the paper P delivered from the fixing unit 21 is directed rearward and upward along the conveyance guide 23. It is conveyed and discharged to a discharge tray 27 formed on the upper surface of the printer casing 2.

  By the way, in the image forming apparatus 1, as shown in FIG. 3, a circuit centering on the control unit 3 is formed by electrically connecting the control unit 3 and each unit. The control unit 3 is mainly configured by a CPU (Central Processing Unit) (not shown), and by reading and executing a predetermined program from a ROM (Read Only Memory), a flash memory, or the like (not shown), various types of printing are performed. Process. The control unit 3 includes a storage unit 3M including a RAM (Random Access Memory), a hard disk drive, a flash memory, and the like, and stores various information in the storage unit 3M.

  The display unit 41 is formed of, for example, a liquid crystal panel, and is provided on the upper portion of the printer housing 2 (FIG. 1), and displays various information to be notified to the user based on the control of the control unit 3. The high-voltage power supply circuit 42 generates a high-voltage power supply based on the control of the control unit 3 and supplies it to the supply roller 35 and the like of the image forming unit 17 (FIG. 2). Based on the control of the control unit 3, the low-voltage power circuit 43 generates a relatively low voltage power source based on an AC commercial power source supplied from the outside and supplies the power source to each unit.

  The registration sensor 11, the writing sensor 12, and the discharge sensor 26 are all connected to the control unit 3, and notify the control unit 3 of the detection result of the paper P. The control unit 3 performs predetermined signal processing on the image data supplied from a host device (not shown), and sequentially supplies the image data to the print head 33 for each line. As a result, the print head 33 can cause each LED to emit light appropriately with a light emission pattern corresponding to the image data.

  The drum driving motor 44 rotates the photosensitive drum 38 and the like appropriately by supplying a driving force to the photosensitive drum 38 (FIG. 2) and the like of the image forming unit 17 based on the control of the control unit 3. The belt motor 45 supplies the driving force to the transfer belt driving roller 14 based on the control of the control unit 3, thereby rotating the transfer belt driving roller 14 and causing the transfer belt 16 (FIG. 1) to travel.

  The transport motor 46 transmits a driving force to the pickup roller 6 and the paper feed roller pair 8 via the paper feed clutch 47 and a driving force to the resist roller pair 9 via the registration clutch 48 based on the control of the control unit 3. , And further, a driving force is transmitted to the conveying roller pair 10. Further, the paper feed clutch 47 and the registration clutch 48 each switch whether to transmit the driving force based on the control of the control unit 3. Thereby, the conveyance motor 46 can rotate each roller suitably.

  The fixing motor 49 rotates the transmission roller pair 24 and the discharge roller pair 25 by transmitting a driving force based on the control of the control unit 3. Further, the fixing motor 49 transmits driving force to the fixing unit 21, thereby transmitting driving force to a roller or the like (which will be described later in detail) provided in the fixing unit 21 for rotation.

[2. Configuration of fixing unit]
Next, the configuration of the fixing unit 21 will be described with reference to FIG. The fixing unit 21 is roughly divided into a heater 51, a thermistor 52 and a heating belt 53 (hereinafter collectively referred to as a belt heating unit 54) disposed on the upper side of the conveyance path U, and a lower side of the conveyance path U. The pressure roller 55 is arranged.

  The heater 51 as a heating unit is formed in a rectangular parallelepiped shape that is long in the left-right direction and short in the up-down direction, that is, is made of stainless steel or ceramic as a base material, that is, is elongated in the left-right direction and thin in the up-down direction. A predetermined resistance material is disposed on the lower surface of the heater 51 so as to form a predetermined pattern, and these are electrically connected. Thus, the heater 51 forms a so-called planar heater, and the lower surface can be heated by supplying a current having a predetermined voltage from the low-voltage power supply circuit 43 (FIG. 3). Further, the heater 51 is supported near the left and right ends by a holder (not shown), and its position is fixed.

  The thermistor 52 as a temperature detection unit is attached in contact with the upper surface of the heater 51, and changes the resistance value according to the temperature of the heater 51. The controller 3 can detect a change in resistance value in the thermistor 52 as a change in voltage or current, and can detect the temperature of the heater 51 based on this change.

  The heating belt 53 is an endless belt formed in a hollow cylindrical shape with the central axis extending in the left-right direction as a whole, and the lower surface of the heater 51 is in contact with the vicinity of the lower end of the inner peripheral surface thereof. Yes. For this reason, the heating belt 53 is locally heated by the heater 51. The heating belt 53 uses, for example, a polyimide resin as a base material, and the heat capacity is suppressed to be small by forming the polyimide resin sufficiently thin. The heating belt 53 is provided with an elastic layer made of silicone rubber as an intermediate layer, and a surface layer made of a fluorine resin such as PFA (perfluoroalkoxyalkane) is provided on the outer peripheral side.

  The pressure roller 55 is formed in a cylindrical shape having a central axis along the left-right direction, and has a rotation axis along the left-right direction at the center. The rotating shaft is rotatably supported by a predetermined support member, and the driving force is transmitted from the fixing motor 49 via a transmission mechanism (not shown) that transmits the driving force by a combination of a plurality of gears. It has become.

  The pressure roller 55 is located directly below the belt heating unit 54, and the upper end of the pressure roller 55 is brought into contact with the lower end of the belt heating unit 54 on the conveyance path U. The pressure roller 55 is made of foamed silicone rubber or the like and has sufficient elasticity.

  With this configuration, when the driving force is transmitted from the fixing motor 49, the pressure roller 55 rotates about the rotation axis. At this time, since the friction between the pressure roller 55 and the heating belt 53 acts, the heating belt 53 can be rotated, that is, run along the circumferential direction. At this time, when the paper P is transported on the transport path U, the pressure roller 55 can press the paper P against the belt heating unit 54.

  By the way, in the fixing unit 21, when the fixing motor 49 is rotated to transmit the driving force to the pressure roller 55, the heating belt 53 travels along with the rotation of the pressure roller 55. Friction occurs between the first and second members. For this reason, in the fixing motor 49, the value of the generated torque is determined according to the friction generated between the heating belt 53 and the heater 51.

  Therefore, in the fixing unit 21, heat-resistant lubricating grease is applied as a lubricant to the inner peripheral surface of the heating belt 53. Thereby, in the fixing unit 21, in a state where the heating belt 53 becomes high temperature due to the heating of the heater 51, the friction between the heating belt 53 and the heater 51 is reduced to improve the sliding property, that is, smoothly. It can be slid.

  Here, in the fixing unit 21, when heating of the heating belt 53 by the heater 51 is started at a room temperature while rotating by transmitting a driving force from the fixing motor 49 to the pressure roller 55, Assume the generated torque. At this time, the control unit 3 controls the supply of power to the heater 51 based on the temperature detected by the thermistor 52. Accordingly, the temperature detected by the thermistor 52 changes so as to maintain this target temperature after approaching a predetermined target temperature as shown in FIG. 5 as a temperature characteristic curve ST1 showing the relationship between time and temperature. To do.

  If the lubricating grease is not applied between the heating belt 53 and the heater 51, the torque generated in the fixing motor 49 initially has a certain magnitude as shown as a torque characteristic curve SQ1 in FIG. Although it decreases slightly as the temperature rises over time, it remains almost constant.

  On the other hand, when the grease for lubrication is applied, the torque generated in the fixing motor 49 is initially a sufficiently large value as shown by the torque characteristic curve SQ2 in FIG. , It decreases significantly, and becomes sufficiently smaller than the case where the lubricating grease is not applied.

  With this configuration, the fixing unit 21 heats the heating belt 53 by the heater 51 to increase the temperature, and rotates the pressure roller 55 by the force transmitted from the fixing motor 49 via the transmission mechanism. As a result, when the toner image is transferred and conveyed along the conveyance path U, the fixing unit 21 sandwiches the sheet P between the outer peripheral surfaces of the heating belt 53 and the pressure roller 55 and comes into contact therewith. As a result, the toner image can be fixed on the paper P by applying heat and pressure, and then sent backward.

[3. Configuration of torque detector]
Next, the configuration of the torque detector 60 (FIG. 4) that detects the torque generated in the fixing motor 49 will be described. The torque detection unit 60 includes a current detection resistor 61, a comparator 62, and voltage dividing resistors 63 and 64. Incidentally, a fixing motor voltage VM set based on the control of the control unit 3 is applied to the fixing motor 49, and the fixing motor 49 rotates at a driving speed corresponding to the fixing motor voltage VM.

  The current detection resistor 61 has a predetermined resistance value. One end of the current detection resistor 61 is connected to the fixing motor 49 and the other end is grounded. A current having a magnitude corresponding to a load generated in the fixing motor 49, a so-called load current. Is supplied. For this reason, the voltage corresponding to the magnitude of the load current, that is, the voltage corresponding to the magnitude of the torque generated in the fixing motor 49 is applied to the connection point P1 connected to the fixing motor 49 side of the current detection resistor 61. Appears. This connection point P1 is connected to the inverting input terminal of the comparator 62, and supplies a torque detection signal S1 representing this voltage to the comparator 62.

  On the other hand, each of the voltage dividing resistors 63 and 64 has a predetermined resistance value, one end of each is connected at the connection point P2, and the other end of the voltage dividing resistor 63 is connected to a predetermined reference voltage VR. The other end of the voltage dividing resistor 64 is grounded. That is, the voltage dividing resistors 63 and 64 divide the reference voltage VR according to the ratio of the resistance values of the reference voltage VR. The connection point P2 is connected to the non-inverting input terminal of the comparator 62, and supplies a torque reference signal S2 representing the voltage at the connection point P2 to the comparator 62.

  The comparator 62 compares the torque reference signal S2 input to the non-inverting input terminal with the torque detection signal S1 input to the inverting input terminal, and generates a torque comparison result signal S3 representing the comparison result. Supply to the control unit 3. The torque comparison result signal S3 is a logical value that is at a high level if the torque reference signal S2 is larger and is at a low level if the torque detection signal S1 is larger.

  As a result, if the torque comparison result signal S3 is at a high level, the control unit 3 causes the torque detection signal S1 to be relatively small. Therefore, the torque generated in the fixing motor 49 is relatively small, and the heating belt 53 and the heater 51 It can be recognized that the viscosity of the lubricating grease present in between is relatively low. Further, if the torque comparison result signal S3 is at a low level, the control unit 3 indicates that the torque detection signal S1 is relatively large, and thus the torque generated in the fixing motor 49 is relatively large. It can be recognized that the viscosity of the lubricating grease present in the is relatively high.

  As described above, the torque detection unit 60 converts the torque generated in the fixing motor 49 into a torque corresponding to the torque reference signal S2 (hereinafter referred to as a reference torque) based on the comparison result between the torque detection signal S1 and the torque reference signal S2. The result of comparison with (calling) can be acquired.

[4. Fixing preparation process]
By the way, in the fixing unit 21, when the rotation of the fixing motor 49 is started at room temperature in order to perform the fixing process, the torque generated in the fixing motor 49 is reduced and transmitted by performing preheating as in Patent Document 1. It is possible to reduce the damage to the mechanism.

  In this case, the fixing unit 21 first heats the heater 51 while the pressure roller 55 is stopped, and raises the temperature of the lubricating grease to lower the viscosity, whereby the friction between the heating belt 53 and the heater 51 is increased. The rotation of the fixing motor 49 is started after reducing the above.

  However, in the fixing unit 21, when preheating is performed, as described above, “temperature unevenness” in which the temperature locally varies depending on the position in the circumferential direction on the heating belt 53 occurs, and the sheet P is subjected to fixing processing in the subsequent fixing process. There is a possibility of uneven glossiness in the image to be fixed. Here, the relationship between the magnitude of the torque of the fixing motor 49 and the degree of occurrence of temperature unevenness when the preheating temperature is changed can be summarized as a table TBL1 shown in FIG.

  That is, in the fixing unit 21, when the preheating temperature is relatively high, the torque of the fixing motor 49 can be suppressed, that is, damage to the transmission mechanism can be suppressed, but the occurrence degree of temperature unevenness increases. On the other hand, in the fixing unit 21, when the preheat temperature is relatively low, the degree of occurrence of temperature unevenness can be suppressed, but on the other hand, the torque of the fixing motor 49 increases and damage to the transmission mechanism also increases. Thus, in the fixing unit 21, there is a trade-off relationship between the magnitude of the torque of the fixing motor 49 and the degree of occurrence of temperature unevenness.

  In the fixing unit 21, the magnitude of the generated torque differs depending on the driving speed when the fixing motor 49 is first rotated, that is, the initial speed, and the warm-up time, that is, heating of the heater 51 is started. Then, the time until the heating belt 53 reaches a temperature at which the toner can be substantially fixed over the entire circumference is also different. Here, when the initial speed of the fixing motor 49 is varied, the relationship between the magnitude of the torque of the fixing motor 49 and the length of the warm-up time can be summarized as a table TBL2 shown in FIG. 6B. .

  That is, in the fixing unit 21, when the initial speed of the fixing motor 49 is relatively slow, the torque of the fixing motor 49 can be suppressed, that is, damage to the transmission mechanism can be suppressed, but the warm-up time becomes long. On the other hand, when the initial speed of the fixing motor 49 is relatively fast, the torque of the fixing motor 49 increases and damage to the transmission mechanism also increases. Thus, in the fixing unit 21, there is a trade-off relationship between the magnitude of the torque of the fixing motor 49 and the warm-up time.

  Accordingly, the control unit 3 performs fixing preparation processing in which rotation of the fixing motor 49 is started and preparation of fixing processing by the fixing unit 21 is performed in consideration of these trade-off relationships. In this fixing preparation processing, preheating by the heater 51 is started according to the preheating processing procedure RT1 shown in FIG. 7 as the preceding processing, and then driving of the fixing motor 49 is started according to the initial driving processing procedure RT2 as the following processing. It has become.

[4-1. Preheat treatment]
When receiving a print instruction or image data from a host device (not shown), the control unit 3 starts a preheat processing procedure RT1 (FIG. 7) and proceeds to step SP1. In step SP1, the control unit 3 determines whether or not the temperature of the upper surface of the heater 51 is lower than a predetermined temperature T0 (for example, 50 [° C.]) based on the detected temperature detected by the thermistor 52.

  If an affirmative result is obtained here, this means, for example, that sufficient time has passed since the last printing process was completed and heating of the fixing unit 21 was completed, and the temperatures of the heater 51 and the heating belt 53 were Since it is relatively low, it indicates that preheating should be performed before the rotation of the fixing motor 49 is started. At this time, the control unit 3 moves to the next step SP2 to start the preheating by heating the heater 51, and moves to the next step SP3.

  In step SP3, the control unit 3 determines whether or not the detected temperature obtained from the thermistor 52, that is, the temperature of the upper surface of the heater 51 has reached a predetermined preheat temperature T1 (for example, 80 [° C.]). If a negative result is obtained here, the control unit 3 waits for the detected temperature to reach the preheat temperature T1 by repeating this step SP3.

  On the other hand, if a positive result is obtained in step SP3, this means that the upper surface of the heater 51 has reached the preheat temperature T1, and therefore the temperature of the lubricating grease applied in the vicinity of the heater 51 is also equal to the preheat temperature T1. It indicates that the temperature has risen to a near temperature. In this case, in the fixing unit 21, the viscosity of the lubricating grease is sufficiently lowered between the heater 51 and the heating belt 53, so that the torque generated in the fixing motor 49 for rotating the pressure roller 55 is also sufficiently small. Become. At this time, the control unit 3 moves to the next step SP4.

  If a negative result is obtained in step SP1, this means that, for example, the elapsed time since the last printing process was completed and heating of the fixing unit 21 was completed is relatively short. This indicates that it is not necessary to perform preheating before the rotation of the fixing motor 49 is started because the temperature is relatively high. At this time, the controller 3 proceeds to the next step SP4 without performing preheating.

  In step SP4, the control unit 3 ends the preheat processing procedure RT1 in order to end the preheating and start the next initial drive processing.

[4-2. Initial drive processing]
Subsequently, the control unit 3 starts an initial drive processing procedure RT2 (FIG. 8), proceeds to step SP11, and applies a predetermined voltage to the fixing motor 49, thereby causing the fixing motor 49 to move at a predetermined initial driving speed V0. Rotate and move to next step SP12. Incidentally, the initial drive speed V0 is a value that becomes, for example, 50 [mm / sec] when converted into the travel speed of the peripheral side surface of the rotating pressure roller 55, that is, the travel speed of the heating belt 53 that travels. Yes.

  Here, when the preheat processing procedure RT1 is started as a time point TM0 and the time point when a positive result is obtained in step SP3 is a time point TM1, the relationship between the passage of time and the temperature in the fixing unit 21 is graphed. It can be expressed as a temperature characteristic curve ST11 shown in FIG.

  That is, the temperature characteristic curve ST11 monotonously increases substantially linearly from time point TM0 to time point TM1, then increases again after turning to decrease at time point TM1. At this time, in the fixing unit 21, when the fixing motor 49 starts to rotate at the time point TM1 and the running of the heating belt 53 starts, a portion that has not been heated until then comes into contact with the heater 51. Although the temperature drops, it starts to increase.

  Further, when the relationship between the passage of time in the fixing unit 21 and the driving speed of the fixing motor 49 is graphed, it can be expressed as a speed characteristic curve SV11 shown in FIG. 9B. That is, the speed characteristic curve SV11 has a speed “0” from the time point TM0 to the time point TM1, while the speed characteristic curve SV11 becomes the initial drive speed V0 after the time point TM1.

  Further, if the relationship between the passage of time and the torque in the fixing motor 49 is graphed, it can be expressed as a torque characteristic curve SQ11 shown in FIG. This torque characteristic curve SQ11 becomes a relatively high torque value TQ11 immediately after the time point TM1 when the fixing motor 49 starts to rotate at the initial drive speed V0, that is, immediately after the heating belt 53 starts to travel, and the temperature rises with time. Then it goes down.

  In step SP12, the control unit 3 performs feedback control using the predetermined fixing temperature T2 as a target temperature as constant temperature control of the heater 51, that is, control that maintains the detected temperature obtained by the thermistor 52 in accordance with the fixing temperature T2. Start and move to next step SP13. Incidentally, the fixing temperature T2 is an appropriate temperature when the fixing process is performed, and is, for example, 180 [° C.].

  In step SP13, the control unit 3 determines whether or not a predetermined time TS (for example, 20 [ms]) has elapsed since the start of the constant temperature control of the heater 51, that is, from the time point TM1 in FIG. If a negative result is obtained here, the control unit 3 waits for the time TS to elapse by repeating this step SP13.

  On the other hand, if an affirmative result is obtained in step SP13, the control unit 3 moves to the next step SP14, whether or not the torque comparison result signal S3 is at a high level, that is, the torque detection signal S1 is smaller than the torque reference signal S2. It is determined whether or not. If a negative result is obtained here, this means that the torque detection signal S1 is larger than the torque reference signal S2, and the torque generated in the fixing motor 49 is relatively large. Indicates that it should not be increased. That is, this means that the temperature of the lubricating grease rises with the passage of time, the viscosity of the grease decreases, and the torque must be lowered. At this time, the control unit 3 moves to the next step SP15.

  In step SP15, the control unit 3 performs a process in preparation for executing the preheat processing procedure RT1 (FIG. 7) next. Specifically, the control unit 3 adds a predetermined temperature difference value ΔT (for example, 5 [° C.]) to the preheat temperature T1, and also determines a predetermined speed difference value ΔV (for example, 5 [mm / sec]) from the initial driving speed V0. Then, the process returns to step SP13 again.

  On the other hand, if a positive result is obtained in step SP14, this means that the torque generated in the fixing motor 49 has become sufficiently small because the temperature of the lubricating grease has sufficiently increased and its viscosity has sufficiently decreased. Represents. This indicates that the torque generated in the fixing motor 49 is lower than the reference torque TQ2 corresponding to the torque reference signal S2, as indicated by the torque characteristic curve SQ11 in FIG. At this time, the controller 3 proceeds to the next step SP16.

  In step SP16, the control unit 3 changes the driving speed of the fixing motor 49 from the initial driving speed V0 to a larger intermediate driving speed V1, and proceeds to the next step SP17. Incidentally, the intermediate drive speed V1 is, for example, 100 [mm / sec] in terms of the running speed of the heating belt 53, and is larger (that is, faster) than the initial drive speed V0 (50 [mm / sec]).

  Here, assuming that the time point when the driving speed of the fixing motor 49 is changed to the intermediate driving speed V1 is a time point TM2, the speed characteristic curve SV11 (FIG. 9B) is bent into a rectangular shape at this time point TM2 and the intermediate driving speed. V1.

  Accordingly, as shown in temperature characteristic curve ST11 (FIG. 9B), the fixing unit 21 temporarily decreases the temperature of the heater 51 detected by the thermistor 52 in the same manner as immediately after the time point TM1. It starts to increase again. Further, the torque generated in the fixing motor 49 at this time is temporarily increased to form a peak as in the torque characteristic curve SQ11 (FIG. 9A), immediately after the time point TM1, and then again. It starts to decrease.

  In step SP17, similarly to step SP13, the control unit 3 determines whether or not a predetermined time TS has elapsed since the driving speed of the fixing motor 49 was changed to the intermediate driving speed V1, that is, from the time point TM2. If a negative result is obtained here, the control unit 3 waits for the time TS to elapse by repeating this step SP17.

  On the other hand, if an affirmative result is obtained in step SP17, the control unit 3 moves to the next step SP18, and similarly to step SP14, whether or not the torque comparison result signal S3 is at the high level, that is, the torque detection signal S1 is the torque. It is determined whether or not it is smaller than the reference signal S2. If a negative result is obtained here, this means that the torque detection signal S1 is larger than the torque reference signal S2, and the torque generated in the fixing motor 49 is relatively large. It means that it should wait for the viscosity to decrease and the torque to decrease. At this time, the control unit 3 returns to step SP17 again and waits for the time TS to elapse again.

  On the other hand, if an affirmative result is obtained in step SP18, this means that, as in the case where an affirmative result is obtained in step SP14, the temperature of the lubricating grease is sufficiently increased and the viscosity thereof is sufficiently decreased. This shows that the torque generated in is sufficiently small. This indicates that the torque generated in the fixing motor 49 is lower than the reference torque TQ2 corresponding to the torque reference signal S2, as indicated by the torque characteristic curve SQ11 in FIG. At this time, the controller 3 proceeds to the next step SP19.

  In step SP19, the control unit 3 changes the driving speed of the fixing motor 49 from the intermediate driving speed V1 to a higher fixing driving speed V2, and proceeds to the next step SP20. Here, assuming that the time point when the driving speed of the fixing motor 49 is changed to the fixing driving speed V2 is a time point TM3, the speed characteristic curve SV11 (FIG. 9B) is rectangular at the time point TM3 as in the case of the time point TM2. Bending to the fixing driving speed V2.

  Accordingly, in the fixing unit 21, as shown as a temperature characteristic curve ST11 (FIG. 9B), the temperature of the heater 51 detected by the thermistor 52 is temporarily similar to immediately after the time point TM1 and immediately after the time point TM2. Then it starts to increase again. Further, at this time, the torque generated in the fixing motor 49 temporarily increases to form a peak as shown immediately after the time point TM1 and immediately after the time point TM2, as shown as a torque characteristic curve SQ11 (FIG. 9A). Then, it starts to decrease again.

  In step SP20, as in steps SP13 and SP17, the control unit 3 determines whether or not a predetermined time TS has elapsed since the driving speed of the fixing motor 49 is changed to the fixing driving speed V2, that is, from the time point TM3. To do. If a negative result is obtained here, the control unit 3 waits for the time TS to elapse by repeating this step SP20.

  On the other hand, when an affirmative result is obtained in step SP20, the control unit 3 moves to the next step SP21, and similarly to steps SP14 and SP18, whether or not the torque comparison result signal S3 is at the high level, that is, the torque detection signal S1. Is smaller than the torque reference signal S2. If a negative result is obtained here, this means that the torque detection signal S1 is larger than the torque reference signal S2, and the torque generated in the fixing motor 49 is relatively large. It means that it should wait for the viscosity to decrease and the torque to decrease. At this time, the control unit 3 returns to step SP20 again and waits for the time TS to elapse again.

  On the other hand, if an affirmative result is obtained in step SP21, this means that, as in the case where an affirmative result is obtained in steps SP14 and SP18, the temperature of the lubricating grease is sufficiently increased and its viscosity is sufficiently lowered, thereby fixing. This shows that the torque generated in the motor 49 has become sufficiently small. This indicates that the torque generated in the fixing motor 49 is lower than the reference torque TQ2 corresponding to the torque reference signal S2, as in the torque characteristic curve SQ11 (FIG. 9A). At this time, the controller 3 proceeds to the next step SP22.

  In step SP22, the control unit 3 determines whether or not the detected temperature obtained from the thermistor 52, that is, the upper surface temperature of the heater 51 has reached the fixing temperature T2. If a negative result is obtained here, the controller 3 waits for the temperature of the upper surface of the heater 51 to reach the fixing temperature T2 by repeating this step SP22. On the other hand, if a positive result is obtained in step SP22, this indicates that the heater 51 and the heating belt 53 have reached a temperature suitable for the fixing process, as at the time point TM4 in FIG. At this time, the control unit 3 moves to the next step SP23.

  In step SP23, the control unit 3 determines whether or not the heating belt 53 has traveled one lap since the start of travel in step SP11. If a negative result is obtained here, the control unit 3 waits for the heating belt 53 to finish one round by repeating this step SP23. On the other hand, if an affirmative result is obtained in step SP23, this is heated by the heater 51 over the entire circumference as the heating belt 53 travels, and the temperature unevenness at each circumferential position is reduced. Represents that. At this time, the control unit 3 moves to the next step SP24 and ends the initial drive processing procedure RT2.

  Incidentally, when the initial drive processing procedure RT2 is completed, the control unit 3 forms a toner image in the image forming unit 17 (FIGS. 1 and 2), transfers it to the paper P, and supplies it to the fixing unit 21 for fixing. Let

[5. Effect]
In the above configuration, the control unit 3 of the image forming apparatus 1 according to the present embodiment starts the preheating processing procedure RT1 (FIG. 7) and the initial driving processing procedure RT2 (FIG. 8) when the fixing unit 21 starts the fixing processing. To do.

  If the fixing unit 21 directly switches from the state where the driving speed of the fixing motor 49 is stopped at the time point TM1 (FIG. 9A) to the fixing driving speed V2 (FIG. 9B), the same as in FIG. As indicated by the broken line in FIG. 9, the torque characteristic curve SQ2 gradually decreases after the torque becomes a relatively large value immediately after the time point TM1. That is, in this case, an extremely large torque is generated immediately after the time point TM1, and there is a possibility that the transmission mechanism that transmits the driving force from the fixing motor 49 may be damaged.

  On the other hand, the control unit 3 according to the present embodiment heats the fixing motor 49 at a predetermined driving speed while heating the lubricating grease by the heater 51 and reducing the viscosity in step SP14 of the initial driving processing procedure RT2. The heating belt 53 is caused to travel by operating. In this state, the control unit 3 switches the driving speed of the fixing motor 49 to a higher speed every time the torque detection signal S1 indicating the magnitude of the torque generated in the fixing motor 49 is lower than the torque reference signal S2. did.

  In other words, the control unit 3 monitors the torque generated in the fixing motor 49, and changes the driving speed of the fixing motor 49 by a relatively small fluctuation range every time the torque sufficiently decreases. I tried to increase it.

  For this reason, the control unit 3 suppresses the increase width when the torque temporarily increases immediately after switching the driving speed of the fixing motor 49 as compared with the case where the driving speed is switched with a large fluctuation width. (FIG. 9A). As a result, the image forming apparatus 1 can suppress the torque generated in the fixing motor 49 to a sufficiently small value, so that damage is given to the transmission mechanism that transmits the driving force from the fixing motor 49 to the pressure roller 55 of the fixing unit 21. It can be kept small.

  Further, the controller 3 ends preheating when the temperature detected by the thermistor 52 reaches a preheating temperature T1 (80 [° C.]) lower than the fixing temperature T2 (180 [° C.]) in the preheating processing procedure RT1. The rotation of the fixing motor 49 is started. As a result, the image forming apparatus 1 can suppress the degree of temperature unevenness smaller than the case of continuing preheating until the fixing temperature T2 is reached (FIG. 6A), and the degree of occurrence of uneven glossiness in the fixing process. Can be reduced.

  Further, in the initial drive processing procedure RT2 (FIG. 8), the control unit 3 compares the torque detection signal S1 with the torque reference signal S2 in steps SP14, SP18, and SP21, respectively, and whether the torque has sufficiently decreased. Judged whether or not. For this reason, in the image forming apparatus 1, in any comparison process, the value of the torque comparison result signal S3 generated as a comparison result by the comparator 62 of the torque detector 60 (FIG. 4) may be referred to. There is no need to provide a dedicated comparison circuit for each, or to perform other complicated arithmetic processing.

  In addition to this, the controller 3 adds the temperature difference value ΔT to the preheat temperature T1 and subtracts the speed difference value ΔV from the initial drive speed V0 in step SP15 of the initial drive processing procedure RT2 (FIG. 8). did. As a result, when the image forming apparatus 1 next executes the preheating processing procedure RT1, the temperature of the heater 51 and the like is increased to the preheating temperature T1 higher than this time by preheating, and the fixing motor 49 is initially driven lower than this time. It can be rotated at a speed V0. Accordingly, the control unit 3 can increase the temperature of the lubricating grease and reduce the traveling speed of the heating belt 53 in the next preheating process, as shown in FIGS. 6 (A) and 6 (B). Due to the relationship, the torque of the fixing motor 49 can be further reduced.

  In addition, in the preheating processing procedure RT1 (FIG. 7), the control unit 3 does not perform preheating when the temperature detected by the thermistor 52 in the first step SP1 is higher than the temperature T0. Accordingly, when the temperature is sufficiently high and the viscosity of the lubricating grease is sufficiently lowered, the image forming apparatus 1 omits the preheating so that the waiting time until the fixing unit 21 can perform the fixing process is reduced. It can be shortened.

  According to the above configuration, the control unit 3 of the image forming apparatus 1 according to the present embodiment operates the fixing motor 49 and runs the heating belt 53 while heating the lubricating grease by the heater 51 to reduce the viscosity. Whenever the torque detection signal S1 falls below the torque reference signal S2, the driving speed of the fixing motor 49 is switched to a higher speed. As a result, the image forming apparatus 1 can sufficiently suppress the torque generated in the fixing motor 49 while gradually heating each part of the heating belt 53, and thus can effectively reduce the occurrence of uneven gloss in the fixing process. At the same time, damage to the transmission mechanism that transmits the driving force from the fixing motor 49 to the pressure roller 55 of the fixing unit 21 can be reduced.

[6. Other Embodiments]
In the above-described embodiment, in the initial drive processing procedure RT2 (FIG. 8), in each of the processes in steps SP14, SP18 and SP21, the torque detection signal S1 is compared with the torque reference signal S2, that is, the same. The case where it is determined whether or not the torque has sufficiently decreased is described using the comparison criteria. However, the present invention is not limited to this. For example, in each process, the comparison reference may be different from each other, for example, the value of the signal to be compared with the torque detection signal S1 is different. In this case, for example, a circuit similar to the torque detection unit 60 may be provided for each signal to be compared, or the torque detection signal S1 is converted into a digital value by analog / digital conversion processing and stored in advance. You may compare with each reference value. Further, in this case, the reference value may be changed according to the temperature detected by the thermistor 52.

  Further, in the above-described embodiment, the case where the fixing motor 49 is rotated at the initial driving speed V0 after performing preheating when the temperature is relatively low in the preheating processing procedure RT1 (FIG. 7) has been described. However, the present invention is not limited to this. For example, the fixing motor 49 may be rotated at the initial driving speed V0 without performing preheating regardless of the temperature. In this case, the torque generated in the fixing motor 49 may be reduced by setting the initial drive speed V0 to a lower value.

  Furthermore, in the above-described embodiment, a case has been described in which, in step SP3 of the preheat processing procedure RT1 (FIG. 7), the fact that the temperature has reached the preheat temperature T1 is a condition for ending preheat. However, the present invention is not limited to this, and preheating may be terminated when various conditions are satisfied, for example, when preheating is terminated when a predetermined preheating time has elapsed since the start of preheating. In this case, for example, at the stage where preheating is started in step SP2, feedback control using the fixing temperature T2 as the target temperature may be started, and step SP12 may be omitted.

  Furthermore, in the above-described embodiment, the case where the preheat temperature T1 is increased and the initial drive speed V0 is decreased for the next preheat process in step SP15 of the initial drive process procedure RT2 (FIG. 8) has been described. However, the present invention is not limited to this. For example, only one of the increase in the preheat temperature T1 and the decrease in the initial drive speed V0 may be performed, or neither may be performed. Alternatively, when a positive result is obtained in step SP14, or when there is no problem in torque when a plurality of print jobs are continuously executed, the decrease in the preheat temperature T1 and the increase in the initial drive speed V0 are caused. At least one of them may be performed.

  Further, in the above-described embodiment, a case has been described in which the standby is performed for the same time TS (20 [ms]) in steps SP13, SP17 and SP20 of the initial drive processing procedure RT2 (FIG. 8). However, the present invention is not limited to this, and each step may wait for a different time. Alternatively, the standby time may be changed as appropriate, such as setting the standby time according to the temperature detected by the thermistor 52 at that time.

  Further, in the above-described embodiment, a case has been described in which standby is performed until the temperature detected by the thermistor 52 reaches the fixing temperature T2 in step SP22 of the initial drive processing procedure RT2 (FIG. 8). However, the present invention is not limited to this. For example, when the waiting time TS is set to a relatively long time in step SP13 or the like, this step SP22 may be omitted.

  Further, in the above-described embodiment, the case has been described in which it is determined whether or not the heating belt 53 has traveled once in step SP23 of the initial drive processing procedure RT2 (FIG. 8). However, the present invention is not limited to this, and an arbitrary number of rotations such as whether or not the heating belt 53 has rotated two or more times may be used as the determination condition. In this case, by increasing the rotation speed, although time is required, temperature unevenness can be reduced at the start of the fixing process. Further, the timing for accelerating the fixing motor 49 may be synchronized with the rotation period of the heating belt 53.

  Furthermore, in the above-described embodiment, the driving speed of the fixing motor 49 is changed from the stopped state to the initial driving speed V0 (50 [mm / s]), the intermediate driving speed V1 (100 [mm / s]), and the fixing driving speed. The case of increasing in stages in three steps of V2 (150 [mm / s]) has been described. However, the present invention is not limited to this. For example, the intermediate drive speed V1 may be omitted to provide two stages, or further different drive speeds may be set to provide four or more stages. Further, the difference values between the driving speeds may not be equal.

  Further, in the above-described embodiment, the case where the driving speed of the fixing motor 49 is changed stepwise, that is, the case where the speed characteristic curve SV11 (FIG. 9B) bends in a polygonal line shape or a staircase shape has been described. However, the present invention is not limited to this. For example, the driving speed of the fixing motor 49 may be continuously changed so that the speed characteristic curve SV11 (FIG. 9B) draws a curve.

  Further, in the above-described embodiment, the case where the heating belt 53 is heated by the heater 51 (FIG. 3) configured as a planar heater has been described. However, the present invention is not limited to this. For example, the heating belt 53 may be heated by a heating unit having various configurations, such as a heating unit configured by a halogen heater and a reflection plate surrounding the halogen heater. In this case, a part of the heating unit may be brought into contact with the heating belt 53 and lubricating grease may be applied between them.

  Further, in the above-described embodiment, the case where the thermistor 52 detects the vicinity of the heater 51 in the heating belt 53 and the temperature of the heater 51 has been described. However, the present invention is not limited to this, and the temperature of the heater 51 and the like may be detected by a temperature detection unit having various configurations.

  Furthermore, in the above-described embodiment, the case where the thermistor 52 is provided at the position where it contacts the upper surface of the heater 51 has been described (FIG. 3). However, the present invention is not limited to this, and the thermistor 52 may be provided at various positions in contact with or very close to the heater 51.

  Further, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 formed of a printer has been described. However, the present invention is not limited to this. For example, a copier, a facsimile machine, or an MFP (Multi Function Peripheral) having a plurality of functions such as various functions having a function of forming a toner image by an electrophotographic method and fixing it on a sheet. The present invention may be applied to other electronic devices. The present invention is not limited to a device that performs so-called color printing using a plurality of image forming units 17 corresponding to a plurality of colors, and may be applied to a device that performs single color (monochrome) printing with a single image forming unit 17. .

  Further, the present invention is not limited to the above-described embodiment and other embodiments. That is, the scope of the present invention extends to embodiments in which some or all of the above-described embodiments and other embodiments described above are arbitrarily combined, and embodiments in which some are extracted. is there.

  Further, in the above-described embodiment, the image forming unit 17 as the image forming unit, the fixing unit 21 as the fixing unit, the fixing motor 49 and the pressure roller 55 as the driving unit, and the torque detection as the torque detecting unit. The case where the image forming apparatus 1 as the image forming apparatus is configured by the unit 60 and the control unit 3 as the control unit has been described. However, the present invention is not limited to this, and an image forming apparatus may be configured by an image forming unit, a fixing unit, a driving unit, a torque detecting unit, and a control unit having various other configurations.

  The present invention can be used in a printer, an MFP, or the like that prints by forming a toner image by electrophotography and fixing the toner image on a sheet.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3 ... Control part, 17 ... Image forming unit, 21 ... Fixing part, 49 ... Fixing motor, 51 ... Heater, 52 ... Thermistor, 53 ... Heating belt, 54 ... ... belt heating section, 55 ... pressure roller, 60 ... torque detection section, 61 ... current detection resistance, 62 ... comparator, 63, 64 ... partial pressure resistance, P ... paper, RT1 ... preheat Processing procedure, RT2 ... Initial drive processing procedure, S1 ... Torque detection signal, S2 ... Torque reference signal, S3 ... Torque comparison result signal, SQ11 ... Torque characteristic curve, ST11 ... Temperature characteristic curve, SV11 ... Speed characteristic curve, T0 ... temperature, T1 ... preheat temperature, T2 ... fixing temperature, TQ11 ... torque value, V0 ... initial driving speed, V1 ... intermediate driving speed, V2 ... fixing driving speed, ΔT ... ... Temperature difference value ΔV ...... speed difference value.

Claims (10)

An image forming unit for forming a developer image representing an image with a developer;
An endless belt having a lubricant coated on the inner peripheral surface thereof and capable of traveling in the circumferential direction; and a heating unit that abuts on the inner peripheral surface of the belt and locally heats the developer image. A fixing unit for bringing the outer peripheral surface of the belt into contact with the transferred medium;
A drive unit that transmits the driving force to the belt to travel;
A torque detection unit for detecting the torque of the drive unit;
A control unit for controlling the drive unit based on a torque detection result by the torque detection unit,
The control unit changes the driving speed of the driving unit according to the torque detection result of the torque detection unit in an initial driving process in which the heating unit is heated and the belt is driven by the driving unit. An image forming apparatus. 2. The control unit according to claim 1, wherein the control unit increases the driving speed of the driving unit every time the torque detection result of the torque detecting unit falls below a predetermined reference torque in the initial driving process. Image forming apparatus. The image forming apparatus according to claim 2, wherein the control unit sets the reference torque according to the driving speed of the driving unit in the initial driving process. In the initial drive process, when the torque detection result by the torque detection unit is larger than a predetermined reference torque, the control unit sets the drive speed by the drive unit in the next initial drive process to be higher than the current speed. 2. When the torque detection result is smaller than the reference torque, control is performed so that the driving speed by the driving unit in the next initial driving process is increased more than this time. The image forming apparatus described. 2. The image formation according to claim 1, wherein the control unit performs control so that the initial driving process is performed after performing a preheating process in which the driving unit stops the belt and heats the heating unit. 3. apparatus. The fixing unit further includes a temperature detection unit that detects a temperature of the heating unit,
The control unit heats the heating unit to a predetermined preheating temperature in the preheating process based on the detected temperature obtained from the temperature detection unit, and in the initial driving process thereafter, is higher than the preheating temperature, The image forming apparatus according to claim 5, wherein the medium is heated to a fixing temperature at which the outer peripheral surface of the belt is brought into contact with a medium to fix the developer image. The fixing unit further includes a temperature detection unit that detects a temperature of the heating unit,
The control unit ends the preheating process when the temperature detected by the temperature detecting unit reaches a predetermined preheating temperature in the preheating process, and the torque detection result by the torque detecting unit in the initial driving process thereafter. Is larger than a predetermined reference torque, the preheating temperature in the next preheating process is increased more than this time, and when the torque detection result is smaller than the reference torque, the preheating process in the next preheating process is performed. The image forming apparatus according to claim 5, wherein the preheating temperature is controlled to be lower than the current temperature. The control unit terminates the preheating process when a predetermined preheating time has elapsed from the start of heating by the heating unit in the preheating process, and the torque detection result by the torque detection unit in the subsequent initial driving process. Is larger than a predetermined reference torque, the preheating time in the next preheating process is increased from this time, and when the torque detection result is smaller than the reference torque, the preheating process in the next preheating process is performed. The image forming apparatus according to claim 6, wherein the preheating time is controlled to be shorter than the current time. The fixing unit further includes a temperature detection unit that detects a temperature of the heating unit,
6. The control unit according to claim 5, wherein when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature, the control unit performs control so that the pre-heating process is omitted and the initial driving process is performed. Image forming apparatus. A heating step in which the belt is locally heated by a heating unit that is endless and has a lubricant applied to the inner circumferential surface thereof, and abuts on the inner circumferential surface of the belt that can travel in the circumferential direction, in a predetermined fixing unit;
A driving step of running the belt by transmitting a driving force from a predetermined driving unit;
A detection step of detecting the torque of the drive unit by a predetermined torque detection unit;
A control step of controlling a driving speed by the driving unit according to a torque detection result detected in the detecting step by a predetermined control unit;
An image forming step of forming a developer image in which an image is represented by a developer by a predetermined image forming unit;
A fixing control method comprising: a fixing step of bringing the belt into contact with the medium onto which the developer image has been transferred in the fixing unit.

Images