JP7268225B2 - image forming device - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus such as a copier or a printer.

An image forming apparatus that has a plurality of heating elements with different longitudinal lengths and exclusively switches the heating elements to which electric power is supplied by a switching unit such as a relay is disclosed (Patent Document 1). By switching to a heating element having a length corresponding to the size of the recording material and performing the fixing process, it is possible to suppress the temperature rise in the non-sheet-passing area.

Japanese Patent Application Laid-Open No. 2001-100558

However, if an imaging job is completed with power available to the last used heating element and the next imaging job uses a different length heating element, the heater is powered. The heating element must be switched before. As a result, there is a problem that the warm-up time of the fixing section becomes long.

One aspect of the present invention includes an image forming unit that forms an image on a recording material, a rotator, a first heating element having the longest length in the longitudinal direction of the rotator, and a and a heater for heating the rotating body having a plurality of heating elements including a second heating element having a short length in the longitudinal direction, and recording an image with the heat of the heater via the rotating body. a fixing unit for fixing onto a material; a switching unit for switching a power supply line so as to enable power supply to any one of the plurality of heating elements; a detection unit for detecting the temperature of the fixing unit; and a controller that controls whether to switch the power supply line according to a result of temperature detection by the detector, wherein the controller controls whether image formation in response to a first print command is completed. After that, when starting image formation in response to the second print command following the first print command, after image formation in response to the first print command is completed, the second print command is performed. During the period until the image formation is started, if the temperature detection result becomes equal to or lower than a predetermined temperature, power can be supplied to the first heating element before the image formation according to the second print command is started. is to switch the power supply line so that

According to the present invention, in an image forming apparatus having a fixing section configured to be exclusively switchable between a plurality of heat generating elements having different longitudinal lengths, the time required for switching the heat generating elements is reduced, and the fixing section is warmed up. can save time.

1 is a schematic cross-sectional view of an image forming apparatus in Example 1. FIG. 3 is a block diagram showing operations of the image forming apparatus according to the first embodiment; FIG. 2 is a schematic cross-sectional view of the fixing device in Example 1 near the center in the longitudinal direction; FIG. 2 is a schematic front view of a heater in Example 1. FIG. 1 is a schematic cross-sectional view of a heater in Example 1. FIG. 4 is a schematic diagram of a power control circuit of the fixing device 50 in Embodiment 1. FIG. 4 is a flow chart of control in Example 1. FIG. 6 is a flow chart of control in a comparative example; 4 is a schematic diagram of a heater in Example 2. FIG. 10 is a flow chart of control in Example 2. FIG.

[Example 1]
FIG. 1 is a configuration diagram showing an in-line color image forming apparatus, which is an example of an image forming apparatus equipped with a fixing device according to the present invention.

The operation of the electrophotographic color image forming apparatus will be described with reference to FIG.

The 1st, 2nd, 3rd, and 4th stations are stations for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively.

In the first station, 1a is a photosensitive drum as an image carrier. The photosensitive drum 1a is formed by laminating a plurality of layers of functional organic materials, such as a carrier generation layer that generates charges by exposure to light on a metal cylinder, and a charge transport layer that transports the generated charges. Low conductivity and almost insulating. A charging roller 2a as a charging means is brought into contact with the photosensitive drum, and rotates to uniformly charge the surface of the photosensitive drum as the photosensitive drum rotates. A voltage obtained by superimposing a DC voltage or an AC voltage is applied to the charging roller, and the photosensitive drum is charged by discharging in a minute air gap upstream and downstream from the contact nip portion between the charging roller and the surface of the photosensitive drum. . A cleaning unit 3a cleans the transfer residual toner on the photosensitive drum 1a. A developing unit 8a as developing means comprises a developing roller 4a, a non-magnetic one-component toner 5a, and a developer applying blade 7a. The above-mentioned 1a to 8a constitute an integrated process cartridge 9a that can be detachably attached to the image forming apparatus.

An exposure unit 11a is composed of a scanner unit or an LED array for scanning laser light with a polygonal mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a modulated based on an image signal.

The charging roller 2a, the developing roller 4a, and the primary transfer roller 10a are connected to a charging high-voltage power supply 20a, a developing high-voltage power supply 21a, and a primary transfer high-voltage power supply 22a, which are means for supplying voltages, respectively.

The structure described above is the first station, and the second, third, and fourth stations have the same structure. The symbols b, c, and d are attached to each.

The intermediate transfer belt 13 is supported by three rollers, a secondary transfer facing roller 15 , a tension roller 14 and an auxiliary roller 19 , as its stretching members. Only the tension roller is applied with a force in the direction in which the intermediate transfer belt is stretched by a spring, so that an appropriate tension force is maintained on the intermediate transfer belt. The secondary transfer opposing roller 15 is rotated by being driven by a main motor (not shown), and the intermediate transfer belt 13 wound around the outer circumference rotates. The intermediate transfer belt 13 moves in the forward direction at substantially the same speed as the photosensitive drums 1a to 1d. The intermediate transfer belt 13 rotates in the direction of the arrow, and the primary transfer roller 10a is arranged on the opposite side of the photosensitive drum 1a with the intermediate transfer belt 13 interposed therebetween, and rotates following the movement of the belt.

The auxiliary roller 19, tension roller 14 and secondary transfer counter roller 15 are electrically grounded. Since the primary transfer rollers of the second to fourth stations have the same structure as that of the first station, the description thereof will be omitted.

Next, the image forming operation of this embodiment will be described. When the image forming apparatus receives a print (image forming) command in a standby state, the image forming operation is started. The photosensitive drums 1a to 1d, the intermediate transfer belt 13, and the like start rotating in the direction of the arrow at a predetermined process speed by a main motor (not shown). The photosensitive drum 1a is uniformly charged by a charging roller 2a by a power supply 20a, and then an electrostatic latent image is formed according to image information by a scanning beam 12a from an exposure means 11a. The toner 5a in the developing unit 8a is negatively charged by the developer applying blade 7a and applied to the developing roller 4a. A predetermined bias is supplied to the developing roller 4a from a developing high-voltage power supply 21a. Then, when the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing roller 4a, the electrostatic latent image is visualized by the negative toner, and the first toner image is formed on the photosensitive drum 1a. A toner image of a color (yellow in this embodiment) is formed. Stations for other colors operate in the same manner, and while delaying the write signal from the controller at a fixed timing for each color according to the distance between the primary transfer positions of each color, the electrostatic latent image by exposure is transferred to each photosensitive drum. Form on 1a-1d. A DC high voltage having a polarity opposite to that of the toner is applied to the primary transfer rollers 10a to 10d. Through the steps described above, each station transfers the toner image onto the intermediate transfer belt 13 in order, and a multiple toner image is formed on the intermediate transfer belt 13 . After that, the recording material P loaded in the recording material cassette 16 is picked up by a paper feed roller 17 and conveyed to a registration roller 18 by a conveying roller (not shown) in synchronization with formation of a toner image. In synchronization with the toner image on the intermediate transfer belt 13 , the recording material P is conveyed by the registration roller 18 to the transfer nip portion where the intermediate transfer belt 13 and the secondary transfer roller 25 contact each other. A secondary transfer high-voltage power supply 26 applies a bias having a polarity opposite to that of the toner to the secondary transfer roller 25, and the four-color multiplexed toner image carried on the intermediate transfer belt 13 is transferred onto the recording material P in two batches. Next transcribed.

On the other hand, after the secondary transfer is finished, the secondary transfer residual toner remaining on the intermediate transfer belt 13 is cleaned by the cleaning unit 27 . After completing the secondary transfer, the recording material P is conveyed to the fixing device 50, receives the toner image, and is discharged to the discharge tray 30 as an image formed product (print, copy).

FIG. 2 is a block diagram for explaining the operation of the image forming apparatus, and the printing operation of the image forming apparatus will be explained based on this diagram.

The PC 110 serving as a host computer plays a role of issuing a print command to a video controller 91 inside the image forming apparatus and transferring image data of a print image to the video controller 91 .

The video controller 91 converts the image data from the PC 100 into exposure data and transfers it to the exposure control device 93 in the engine controller 92 . The exposure controller 93 is controlled by the CPU 94 to turn on/off the exposure data and control the exposure device 11 . When the CPU 94 receives the print command, it starts the image forming sequence.

The engine controller 92 is equipped with a CPU 94, a memory 94, etc., and performs pre-programmed operations. The high voltage power supply 96 has a charging power supply 20 , a development power supply 21 , a primary transfer power supply 22 and a secondary transfer power supply 26 . Further, the fixing power control unit 97 has a triac 56 as a power control unit and a switching unit 57 that exclusively switches to a heating element that supplies power. Further, the driving device 98 is composed of a main motor 99, a fixing motor 100 and the like. Further, the sensor 101 includes a fixing temperature sensor 9 for detecting the temperature of the fixing device 50 and a paper presence/absence flag sensor 102 for detecting the presence/absence of paper. The CPU 94 acquires the detection result of the sensor 101 in the image forming apparatus and controls the exposure device 11 , the high voltage power supply 96 , the fixing power control device 96 and the driving device 97 . As a result, the electrostatic latent image is formed, the developed toner image is transferred, and the toner image is fixed on the recording material.

Next, the configuration of the fixing device according to this embodiment will be described with reference to FIGS. 3 to 6. FIG. The longitudinal direction is the width direction of the recording material, which is perpendicular to the conveying direction of the recording material P, which will be described later. The longitudinal direction is the same as the longitudinal direction of the film 51 or the rotating shaft direction of the pressure roller.

3 is a schematic cross-sectional view of the fixing device 50, FIG. 4 is a schematic front view of the heater, FIG. 5 is a schematic cross-sectional view of the heater, and FIG. 6 is a schematic circuit diagram of the control section of the fixing device.

From the left side of FIG. 3, the recording material P holding the toner image T is heated while being conveyed in the fixing nip portion N, so that the toner image T is fixed on the recording material. The fixing device 50 in this embodiment includes a cylindrical film 51, a nip forming member 52 that holds the film 51, a pressure roller 53 that forms a nip portion together with the film 51, and a heater 54 for heating the recording material. It is composed of

51 is a fixing film as a heating rotator. In this embodiment, polyimide is used as the base layer. An elastic layer made of silicone rubber and a release layer made of PFA are used on the base layer. Grease is applied to the inner surface of the film 51 in order to reduce the frictional force generated between the film 51 and the nip forming member 52 and heater 54 due to the rotation of the film 51 .

The nip forming member 52 guides the film 51 from the inside and forms a nip portion N with the pressure roller 53 via the film 51 . The nip forming member 52 is a member having rigidity, heat resistance, and heat insulation, and is made of liquid crystal polymer or the like. The film 51 is fitted over the nip forming member 52 .

53 is a pressure roller as a pressure rotating body. The pressure roller 53 has a metal core 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably held at both ends and driven to rotate by a fixing motor 100 (not shown). Also, the film 51 is driven to rotate by the rotation of the pressure roller 53 . That is, the fixing motor 100 transmits driving force for driving the film 51 .

54 is a heater as a heating member. The heater 54 is held by the nip forming member 52 and is in contact with the inner surface of the film 51 .

The heater 54 will be described in detail with reference to FIGS. 4 and 5. FIG. FIG. 5 is a view showing a cross section of the heater 54 taken along the longitudinal center line (line a in FIG. 4) of the heating elements 54b1 and 54b2.

The heater 54 has a substrate 54a, heating elements 54b1 and 54b2, a conductor 54c, contacts 54d1-54d3, and a protective glass layer 54e. Heating elements 54b1 and 54b2, a conductor 54c and contacts 54d1 to 54d3 are formed on the substrate 54a, and a protective glass layer 54e is formed thereon to ensure insulation between the heat generating elements 54b1 and 54b2 and the film 51. . A power supply line 500 supplies power to the heater 54 (heating elements 54b1 and 54b2). The heating elements 54b1 and 54b2 are long in the longitudinal direction of the film 51. As shown in FIG.

The longitudinal length L1 of the heating element 54b1 is the longest among the plurality of heating elements provided in the heater . The longitudinal length L2 of the heating element 54b2 is shorter than the longitudinal length L1 of the heating element 54b1. The longitudinal length L1 of the heating element 54b1 is a length that can fix the widest recording material among standard size recording materials that can be used in the apparatus. The heating element 54b1 is electrically connected to the contacts 54d1 and 54d3 via the conductor 54c, and the heating element 54b2 is electrically connected to the contacts 54d2 and 54d3 via the conductor 54c.

A fixing temperature sensor 59 is located on the opposite side of the substrate 54a to the protective glass layer 54e, is installed at the longitudinal center of the heating elements 54b1 and 54b2, and is in contact with the substrate 54a. The fixing temperature sensor is a thermistor that detects the temperature of the heater 54 and sends the detection result to the CPU 94 .

FIG. 6 is a schematic diagram of a power control circuit of the fixing device 50. As shown in FIG. The power control circuit of the fixing device 50 has heating elements 54 b 1 and 54 b 2 , an AC power supply 55 , a power supply line 500 , a triac 56 and a switching section 57 . The switching unit 57 is provided in the middle of the power supply line 500 that electrically connects the AC power supply 55 and the heating element 54b1 or 54b2.

Reference numeral 56 denotes a triac for energizing/cutting the heating elements 54b1 and 54b2 from the AC power supply 55. FIG. The CPU 94 calculates the electric power required to reach the target temperature from the temperature information notified from the thermistor 59, and instructs the triac 56 to turn on/off.

A switching unit 57 is a C-contact relay in this embodiment. It is configured such that the switching unit 57 exclusively selects which one of the heating element 54b1 and the heating element 54b2 is to be supplied with electric power. The switching unit 57 connects to either one of the contact 54d1 and the contact 54d2, that is, switches the power supply line 500. FIG. The switching unit 57 performs this switching upon receiving a signal from the CPU 94 . Hereinafter, for the sake of convenience, switching the power supply line 500 so that power can be supplied to one heating element out of a plurality of heating elements will be referred to as switching the heating element or selecting the heating element. do. In order to prevent contact welding of the switching portion 57, which is a C-contact relay, switching by the switching portion 57 is desirably performed in a state in which energization (power supply) of the triac 56 to the heating element 54b1 or 54b2 is interrupted. Further, in this embodiment, the switching section 57 is connected to the contact 54d1 when power is not supplied to the switching section 57, such as when the power switch of the image forming apparatus main body is turned off.

Features of this embodiment will be specifically described with reference to FIG. FIG. 7 is a flow chart describing the timing of switching control of the heating elements in this embodiment. Here, paper (recording material) having a width corresponding to the heating element 54b2 is referred to as small size paper (small size recording material), and paper (recording material) having a width corresponding to the heating element 54b1 is referred to as large size paper ( large size recording material).

In this embodiment, regardless of whether or not a print job subsequent to a received print job (image forming job) is received, the switching unit is configured to switch to the heating element having the longest longitudinal length and end the print job. ing. Therefore, it is possible to energize (power supply) the heating element 54b1 without switching the heating element immediately after receiving the print command, so that the warm-up time can be shortened. It does not depend on whether or not the next print job is received, which means that if the print job is not received, the size of the paper to be used is unknown, but the heating element with the longest longitudinal length is switched to. . This is because, at least in the initial stage of a print job in which a plurality of recording materials are printed continuously, using the heating element 54b1 having the longest longitudinal length to perform the fixing process has the following advantages. For example, there is a high frequency of using paper having a maximum width usable in the image forming apparatus or a width close to it. In addition, when a print job is received after the image forming apparatus has been left unused for a long time, the fixability of the longitudinal end portions of the image tends to deteriorate. Therefore, at least at the beginning of the print job, regardless of the paper size, the heat generating element 54b1 having the longest longitudinal length is used for the fixing process, thereby improving the edge fixability. Also, the grease present on the inner surface of the film along the longitudinal direction can be uniformly melted to prevent deformation of the film. Therefore, when a print command is received, if power can be supplied to the longest heating element 54b1, the warm-up time of the fixing device can be shortened. In the configuration of this embodiment, it takes 0.2 seconds from the time when the CPU 94 outputs the switching signal until the switching of the switching unit 57 is completed. .2 seconds shorter.

In this embodiment, since the heating element 54b1 is selected when the print command is received, rotation of the fixing motor 100 and energization of the heating element 54b1 are started (S101). Then, a predetermined number of sheets (three sheets in this embodiment) of the initial print job are fixed using the heating element 54b1 (S102). If the specified number of prints for the print job is equal to or less than the predetermined number of prints, when the specified number of prints is reached (S103), power supply to the heating element 54b1 is stopped (S106), and rotation of the fixing motor 100 is stopped (S107). , the print job is completed in a state in which power can be supplied to the heating element 54b1 (S108).

If the number of prints specified in the print job is not reached even after the predetermined number of prints are completed (S103), the subsequent sequence depends on whether the paper size specified in the print job is large size paper or small size paper. different.

When the large size paper is specified (S104), power is supplied to the heating element 54b1 to perform the fixing process on the fourth and subsequent sheets following the initial three sheets (S105). When the printing of the print job is completed, power is turned off using the triac 56 (S106), the fixing motor 100 is stopped (S107), and the operation ends while power can be supplied to the heating element 54b1 (S108).

On the other hand, if the small size paper is specified (S104), the operation of switching to the heating element 54b2 is performed after the initial fixing process of the three sheets is completed. Specifically, the TRIAC 56 is used to stop (OFF) energization of the heating element 54b1 (S109). Then, the heating element is switched from the heating element 54b1 to the heating element 54b2 by the switching unit 57 (S110), and energization to the heating element 54b2 is started (ON) using the triac 56 (S111). Here, the energization of the triac 56 is stopped in order to prevent contact welding of the switching portion 7, which is a C-contact relay. Further, in this embodiment, the heating element is switched during the interval between the preceding sheet and the succeeding sheet in which there is no sheet in the nip portion N. FIG. After that, a fixing process is performed using the heating element 54b2 (S112). When the specified number of prints of the print job is completed, the power supply to the heating element 54b2 is stopped using the triac 56 (OFF) (S113), and the switching unit 57 switches from the heating element 54b2 to the heating element 54b1 (S114). ). After that, the fixing motor 100 is stopped (S107), and the print job is finished (S108). In this embodiment, the operations of S113 and S114 are performed while the fixing motor 100 is rotating after finishing the fixing process. The switching by the switching unit 57 is preferably performed while the main motor 99 and the fixing motor 100, which are driving sources in the image forming apparatus, are rotating as in the present embodiment. This is to prevent the switching sound of the switching unit 57 from standing out.

Next, the effects of this embodiment will be described. Here, the warm-up time is the period (warm-up period) from when the print command is received until the temperature detected by the thermistor 59 reaches the target temperature (the temperature required to fix the toner image T on the recording material P). ) time. Further, the fixing/conveying time is a period (fixing/conveying period) from when the print command is received until the recording material P reaches the nip portion N of the fixing device. If the warm-up time is longer than the fixing and conveying time, it is necessary to delay the timing of conveying the recording material P to the fixing device after receiving the print command. As a result, the first print output time (FPOT), which is the time from the print command until the first sheet is printed and discharged from the image forming apparatus, becomes longer. If the warm-up time is less than the fixing transport time, the FPOT of the image forming apparatus is determined by the fixing transport time, so the warm-up time does not limit the FPOT. In this embodiment, the temperature of the fixing device 50 before printing is started is 23° C., and the warm-up time of the fixing device 50 when the switching operation of the switching unit 57 is unnecessary is 4.0 seconds. Further, the fixing conveying time was also 4.0 seconds. If it is necessary to switch the heating elements by the switching unit 57 when warming up the fixing device 50, the warm-up time is extended by the switching time. In the case of this embodiment, the time required for switching the heating elements is 0.2 seconds, so the time is 4.2 seconds.

Table 1 shows the necessity of switching the heating elements and the warm-up time when switching the heating elements according to the flowchart shown in FIG.

Here, the standby period is a period in which the fixing motor 100 is stopped after a print job is completed and the apparatus waits until a print command for the next print job is sent. The fixing process period refers to the period from when the first sheet of paper enters the nip portion N until the last sheet of paper in the print job passes through the nip portion N. FIG. The end period means that the power supply to the heaters 54 (heating elements 54b1 and 54b2) is stopped after the fixing process for all the sheets of the print job is completed, and the motors such as the fixing motor 100 are stopped to complete the print job. refers to the period until the end of

As shown in Table 1, the configuration of this embodiment switches the power supply line 500 so that power is supplied to the heating element 54b1 before the end of the print job, thereby receiving the next print job. Sometimes switching by the switching unit becomes unnecessary. Therefore, the warm-up time was 4.0 seconds in each case, and the FPOT could always be minimized. Moreover, since the nip portion N was uniformly warmed in the longitudinal direction during warm-up, the film 51 was not deformed.

In order to compare the present embodiment and the comparative example, the configuration of the comparative example will be described.

<Comparative example>
Descriptions of points that overlap with the first embodiment will be omitted. In this comparative example, the heating elements are not switched at the end of printing. Therefore, if the immediately preceding print job is for large-size paper, the print job is finished in a state where power can be supplied to the heating element 54b1. If the immediately preceding print job is for small size paper, the print job is completed in a state in which power can be supplied to the heating element 54b2. FIG. 8 is a flow chart describing the timing of switching control of the heating elements in this comparative example.

First, information as to whether the paper used in the print job is large size paper or small size paper is obtained by a print command (S201). If it is large size paper, information is acquired as to whether the paper used in the previous print job was large size paper or small size paper (S202). If the immediately preceding print job is for large size paper, the heating element 54b1 is selected, so the fixing motor 100 is turned on to start energizing the heating element 54b1 (S203). If the previous print job is for small size paper, the heating element 54b2 is selected, so the switching unit 57 switches to the heating element 54b1 (S204), energizing the heating element 54b1 and rotating the fixing motor 100. Start (S203). Thereafter, a fixing process is performed using the heating element 54b1 (S205), and after printing of the specified number of prints is completed, the heating element 54b1 is energized and the rotation of the fixing motor 100 is stopped (S206). Then, the print job is finished with the heating element 54b1 selected (S207).

Next, a case where small size paper is selected in S201 will be described. Information is acquired as to whether the previous print job is for large size paper or small size paper (S208). Since the heating element 54b2 is selected for the small size paper, the fixing motor 100 is turned on to start energizing the heating element 54b2 (S209). If the immediately preceding print job is large-size paper, the switching unit 57 switches to the heating element 54b2 (S210), and energization of the heating element 54b2 and rotation of the fixing motor 100 are started (S209). After that, the fixing process is performed using the heating element 54b2 (S211). The operation ends with the selected state (S213).

Table 2 shows the necessity of switching the heating element and the warm-up time in the flow chart shown in FIG.

As shown in Table 2, when small-size paper is specified in the previous print job and large-size paper is specified in the next print job, or when large-size paper is specified in the previous print job and the next print job If the print job is small size paper, the heating elements need to be switched. Since switching of the heating elements by the switching unit is performed during the warm-up period, the warm-up time was 4.2 seconds, which was longer than the time required for switching (0.2 seconds).

As described above, in this comparative example, depending on the circumstances, switching time of the switching unit 57 is required when shifting from the standby period to the warm-up period, and the warm-up time becomes long. As a result, in this comparative example, the warm-up time is rate-limiting for shortening the FPOT.

In addition, in this comparative example, when the paper to be conveyed to the fixing device is small size paper, the heating element 54b2 having a short longitudinal length is selected during the warm-up period, so that the nip portion N is uniform in the longitudinal direction. Difficult to warm up. Therefore, a difference in how the grease applied to the inner surface of the film 51 melts occurs between the heated region and the non-heated region of the film 51 . As a result, a difference in frictional force between the film 51 and the heater 54 occurs in the longitudinal direction, and the film 51 may be deformed and damaged.

Thus, the configuration of Example 1 has the effect of shortening the warm-up time of the fixing device as compared with this comparative example. Furthermore, if the inner surface of the film 51 is coated with grease, the effect of preventing deformation of the film is also obtained.

[Example 2]
Descriptions of points that overlap with the first embodiment will be omitted. The configuration of the fixing device 50 in this embodiment will be described with reference to FIG.

FIG. 9 is a schematic diagram of the heater 54. As shown in FIG. Reference numeral 59 denotes a main thermistor as a temperature detecting member for detecting the temperature of the longitudinal central portion of the heater 54 , and 60 denotes a sub-thermistor as a temperature detecting member for detecting the temperature of the longitudinal end portions of the heater 54 . The main thermistor 59 and the sub-thermistor 60 are provided on the surface of the substrate 54a opposite to the surface on which the protective glass layer 54e is formed, and are in contact with the substrate 54a. The main thermistor 59 is provided in the longitudinal center of the heating elements 54b1 and 54b2, and the sub-thermistor 60 is provided inside the heating element 54b1 and outside the heating element 54b2 in the longitudinal direction.

In this embodiment, during the standby period, the temperatures detected by the main thermistor 59 and the sub-thermistor 60 are constantly monitored, and whether or not to switch the heating elements is determined based on the detected temperatures of the thermistors. When the detected temperature is equal to or lower than a predetermined temperature, the switching unit switches to the longest heating element.

This means that if the fixing device is already warmed up at the timing of receiving the print job, such as when not much time has passed since the previous print job was completed, the warm-up time of the fixing device is short. Therefore, even if the switching unit 57 is switched after receiving a print job, the warm-up time of the fixing device can be prevented from being longer than the fixing transportation time. As a result, the warm-up time can be shortened while reducing the number of switching times of the switching unit 57 . In this embodiment, the CPU 94 monitors the temperature detected by the main thermistor 59 and the temperature detected by the sub-thermistor 60 during the standby period. Then, when either of them is 50° C. or lower, the switching unit 57 switches the power supply line 500 so that the power can be supplied to the heating element 54b1. When both the temperature detected by the main thermistor 59 and the temperature detected by the sub-thermistor 60 are 50° C. or higher, the warm-up time is 4.0 seconds, which is the fixing conveyance time, even if the switching unit 57 performs the switching operation during warm-up. never exceeded.

FIG. 10 is a flow chart describing the timing of switching control of the heating elements in this embodiment. The thermistor temperature referred to here is the detected temperature of the thermistor having the lower detected temperature among the main thermistor 59 and the sub-thermistor 60 .

In this embodiment, the CPU 94 monitors the thermistor temperature during the standby period (S301). When the thermistor temperature becomes 50° C. or less and the heating element 54b2 is selected, the switching unit 57 switches to the heating element 54b1 during the standby period (S302). After that, when the print command is received, if the paper specified in the print job is large size paper, or if the specified paper size is small size paper and the specified number of prints is less than the specified number (three) , do the following: That is, the print job is finished with the heating element 54b1 selected at the end of the print job (S309). However, if the paper specified in the print job is small-size paper and the specified number of prints is 3 or more, the print job ends (S315) even though the heater 54b2 is selected when the print job ends (S315).

Next, a case where a print command is received while the thermistor temperature exceeds 50° C. will be described.

If the paper specified in the print job is large size paper (S318), information is acquired as to whether the selected heating element is the heating element 54b1 or the heating element 54b2 (S319). When the heating element 54b1 is selected, the power supply to the heating element 54b1 and the rotation of the fixing motor 100 are started (ON) without switching the heating element (S320). When the heating element 54b2 is selected, the switching unit 57 switches from the heating element 54b2 to the heating element 54b1, and then energization of the heating element 54b1 and rotation of the fixing motor 100 are started (ON) (S320). At this time, since the fixing device 50 is already warmed up, even if the heating element is switched, the warm-up time is 4.0 seconds or less, which does not limit the FPOT. After that, the fixing process is performed using the heating element 54b1 (S322), and when the designated number of prints is completed, the power supply to the heating element 54b1 and the rotation of the fixing motor are stopped (OFF) while the heating element 54b1 remains selected. , finish the print job (324).

If the paper specified in the print job is small size paper (S318), information is acquired as to whether the selected heating element is the heating element 54b1 or the heating element 54b2 (S325). If the heating element 54b2 is selected, the power supply to the heating element 54b2 and the rotation of the fixing motor 100 are started (ON) (S326). When the heating element 54b1 is selected, the switching unit 57 switches from the heating element 54b1 to the heating element 54b2 (S327), and energization of the heating element 54b2 and rotation of the fixing motor 100 are started (ON). (S326). Thereafter, fixing is performed using the heating element 54b2 (S328). When the designated number of prints is completed, the power supply to the heating element 54b2 is stopped, the rotation of the fixing motor 100 is stopped (S329), and the print job is finished with the heating element 54b2 selected (S330).

As described above, according to the present embodiment, as in the first embodiment, it is possible to shorten the warm-up time of the fixing device. Furthermore, if the inner surface of the film 51 is coated with grease, the effect of preventing deformation of the film is also obtained. In addition to this, by reducing the number of switching times of the switching section 57 compared to the first embodiment, it is possible to reduce the number of switching sounds of the switching section 57 . Moreover, there is an effect of extending the life of the switching portion 57 .

Table 3 shows the necessity of switching the heating element and the warm-up time in the flow chart shown in FIG.

As shown in Table 3, Example 2, like Example 1, has the shortest warm-up time in any case, and is not rate-limiting for FPOT. In addition, deformation of the film 51 did not occur in either case. In addition, the number of switching times of the switching unit 57 can be reduced more than in the first embodiment.

Further, in the second embodiment, the switching operation is performed by the switching unit when the temperature detection means is at or below the predetermined temperature during the standby period. You may take action. In that case, as in the first embodiment, the effect of making the switching sound of the switching unit 57 inconspicuous can be obtained.

Also, in the second embodiment, the switching unit is switched based on the temperature detected by the temperature detection unit, but temperature prediction means may be provided to perform switching based on the predicted temperature. For example, a CPU as temperature predicting means predicts the temperature of the heater based on the number of prints, the size of the heating element used, and the elapsed time since the last printing. Then, when the predicted temperature difference between the longitudinal end portions and the longitudinal center portion of the heater is predicted to be 50° C. or less, the switching portion 57 may be used to switch to the heating element 54b1.

In the second embodiment, both the main thermistor and the sub-thermistor are used to determine the degree of warming of the fixing device, but either one may be used.

Further, as another embodiment, it is conceivable to switch the switching unit 57 to the heating element 54b1 having the longest longitudinal width when the fixing device 50 enters the power saving mode. The power saving mode is a mode in which the engine controller 92 supplies power only to necessary parts or controls to reduce the power to be supplied in order to reduce the power consumption of the image forming apparatus. In the power saving mode, the film unit including the film 51 is separated from the pressure roller 53 . With the configuration as described above, even when a print command is issued from the power saving mode, the same effect as in the first embodiment can be obtained. Further, as in the first embodiment, if the switching unit 57 switches to the heating element 54b1 when the power supply is stopped, it becomes unnecessary to send power to the switching unit 57 in the power saving mode. , the effect of suppressing power consumption can also be obtained.

50 fixing device 51 film 53 pressure roller 54 heater 54a substrate 54b1 heating element 54b2 heating element 57 switching section 100 fixing motor

Claims (8)

an image forming unit that forms an image on a recording material;
A plurality of heating elements including a rotating body, a first heating element having the longest longitudinal length of the rotating body, and a second heating element having a shorter longitudinal length than the first heating element. a heater for heating the rotating body having
a switching unit that switches a power supply line so that power can be supplied to any one of the plurality of heating elements;
a detection unit that detects the temperature of the fixing unit;
an image forming apparatus comprising a control unit that controls whether to switch the power supply line according to a temperature detection result of the detection unit,
When starting image formation in response to a second print command subsequent to the first print command after image formation in response to the first print command is completed, the control unit outputs the first print command. When the temperature detection result is equal to or lower than a predetermined temperature during the period from the end of image formation in response to the second print command to the start of image formation in response to the second print command, An image forming apparatus, wherein the power supply line is switched so that power can be supplied to the first heating element before image formation is started. The controller switches the power supply line according to the size of the recording material according to the second print command unless the temperature detection result is equal to or lower than a predetermined temperature during the period. The image forming apparatus according to claim 1. If the size of the recording material on which the image is formed according to the second print command is the first size, the control unit controls the control unit to perform the first print operation before starting power supply in response to the second print command. The power supply line is switched so that power can be supplied to one heating element, and the size of the recording material on which the image corresponding to the second print command is formed is a second size smaller than the first size. 3. The apparatus according to claim 2, wherein if there is, the power supply line is switched so that power can be supplied to the second heating element before power supply is started in accordance with the second print command. Image forming device. The switching unit is a relay provided in a circuit for supplying power to the heater, and power is supplied from the second heating element to the first heating element while power is not being supplied to the relay. 4. The image forming apparatus according to claim 1, wherein the power supply line is switched so as to enable supply. 5. The apparatus according to any one of claims 1 to 4, further comprising a driving source for transmitting a driving force to said rotating body, wherein said switching unit is switched while said driving source is rotating. Image forming device. 6. The heater according to claim 1, wherein the heater has a substrate, and the first heating element and the second heating element are formed on the substrate. Image forming device. 7. An image forming apparatus according to claim 6, wherein said rotating body is a cylindrical film, and said heater is arranged in an internal space of said film. The fixing unit has a roller forming a nip portion together with the heater through the film,
8. The image forming apparatus according to claim 7, wherein the film is nipped between the heater and the roller, and the image on the recording material is heated through the film at the nip portion.

Images