JP2022032318A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can improve productivity through simple control and prevent faulty fixing of a toner image.SOLUTION: An image forming apparatus 100 comprises: detection means 60 that detects the characteristics of a sheet P conveyed by conveying means 10, 20; and control means 70 that, according to a result of detection performed by the detection mean 60, switches a conveyance speed at which the sheet is conveyed by the conveying means 10, 20 between a plurality of conveyance speeds including a first conveyance speed and a second conveyance speed slower than the first conveyance speed. For the second sheet in an image forming job, the control means 70 controls the conveying means such that the sheet is conveyed at a conveyance speed according to the characteristics of the first sheet detected by the detection means 60, and for the first sheet in the image forming job, controls the conveying means 10, 20 such that after the lapse of a delay time tw from when fixing means 40 reaches a target temperature, the sheet is conveyed at a predetermined conveyance speed faster than the second conveyance speed.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus that forms an image on a sheet.

Generally, an image forming apparatus such as a laser printer transfers a toner image formed on a photoconductor to a sheet, and then heats and pressurizes the toner image on the sheet to fix the toner image on the sheet. In such an image forming apparatus, appropriate fixing conditions for fixing the toner image to the sheet vary depending on the characteristics of the sheet. For example, the fixing conditions of the toner image in the image forming apparatus include the temperature at which the toner image is fixed, the sheet transport speed, and the like. Further, for example, the characteristics of the sheet include the basis weight and the surface property. In such an image forming apparatus, if an attempt is made to fix the toner image under fixing conditions that are not appropriate fixing conditions according to the characteristics of the sheet, the toner image may not be sufficiently fixed on the sheet, resulting in fixing failure. For example, a sheet with a large basis weight has a large heat capacity, so when forming an image on a sheet with a large basis weight, if the toner image is to be fixed under the same fixing conditions as a sheet with a small basis weight, the amount of heat given to the toner will be increased. Insufficient toner image may not be sufficiently fixed on the sheet.

Conventionally, there has been disclosed an image forming apparatus capable of detecting the basis weight of a sheet and reducing the transfer speed of the sheet when the basis weight of the sheet is large to suppress poor fixing of the toner image. See Patent Document 1). The image forming apparatus described in Patent Document 1 temporarily stops the transfer of the sheet after detecting the basis weight of the sheet and before forming the toner image on the sheet. Further, the image forming apparatus described in Patent Document 1 decelerates the rotation of the photosensitive drum while the sheet transfer is stopped when the detected basis weight is large, and the sheet transfer speed is small according to the decelerated photosensitive drum. Resume transport. As a result, the image forming apparatus described in Patent Document 1 fixes the toner image on the sheet having a large basis weight at a lower transfer speed than the sheet having a small basis weight, thereby suppressing the fixing failure of the toner image. I'm trying.

Japanese Unexamined Patent Publication No. 2016-102861

In recent years, there has been a demand for an image forming apparatus capable of suppressing fixing defects while improving productivity by simple control. However, the image forming apparatus described in Patent Document 1 controls acceleration / deceleration separately for the photosensitive drum and each roller for transporting the sheet in order to suppress the fixing failure of the toner image. It's complicated. Further, the image forming apparatus described in Patent Document 1 switches the conveying speed in a state where the conveying of the sheet is stopped after determining the basis weight and the like of the sheet when forming an image on the first sheet. It is difficult to improve productivity.

Therefore, an object of the present invention is to provide an image forming apparatus capable of improving productivity and suppressing poor fixing of a toner image by simple control.

One aspect of the present invention is a transporting means for transporting a sheet, an image forming means for forming an unfixed toner image on the sheet transported by the transporting means, and the image forming means for heating and pressurizing the sheet. The fixing means for fixing the transferred toner image to the sheet, the detecting means for detecting the characteristics of the sheet conveyed by the conveying means, and the conveying speed of the sheet by the conveying means according to the detection result of the detecting means. A control means for switching between a first transport speed and a plurality of transport speeds including a second transport speed slower than the first transport speed, wherein the control means relates to a second sheet of an image forming job. Controls the transport means so that the first sheet detected by the detection means is transported at a transport speed according to the characteristics of the first sheet, and the first sheet of the image forming job is described. An image forming apparatus characterized in that the transporting means is controlled so as to be transported at a predetermined transport speed faster than the second transport speed after a delay time elapses after the fixing means reaches a target temperature. be.

According to the present invention, it is possible to improve productivity and suppress poor fixing of the toner image by simple control.

The schematic diagram of the image forming apparatus which concerns on 1st Embodiment. Sectional drawing which shows the fixing device. The block diagram which shows the control composition of an image forming apparatus. A flowchart showing an image forming job. The flowchart which shows the image formation job which concerns on 2nd Embodiment. The flowchart which shows the image formation job which concerns on 3rd Embodiment.

Hereinafter, the image forming apparatus according to each embodiment will be described with reference to the drawings. Unless otherwise specified, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments are not intended to limit the scope of application of the present technology to those. do not have.

<First Embodiment>
[Rough configuration of image forming apparatus]
FIG. 1 is a schematic view showing an image forming apparatus 100 according to the first embodiment. In the present embodiment, an image forming apparatus 100, which is an electrophotographic laser beam printer for forming an image on a sheet (recording material), will be described as an example. The size and material of the sheet include paper such as plain paper and cardboard, surface-treated sheet materials such as plastic film, cloth, and coated paper, and specially shaped sheet materials such as envelopes and index paper. Different and diverse sheets can be used.

The image forming apparatus 100 includes a sheet feeding unit 10 that feeds a sheet, a sheet conveying device 20 that conveys a sheet, an image forming unit 30 that forms a toner image on the sheet, a fixing device 40 that fixes the toner image on the sheet, and a motor. It includes 50 and a control unit 70. Further, the image forming apparatus 100 includes a sheet sensor 80 that detects the sheet to be conveyed, and a media sensor 60 that detects the characteristics of the sheet to be conveyed.

The sheet feeding section 10 as a transporting means is detachably provided with respect to the main body of the apparatus, and is housed in a feeding cassette 11 as a sheet loading section for loading and storing the sheet P, and a feeding cassette 11. It has a feeding roller 12 for feeding a sheet. The feeding roller 12 as a feeding means rotates while abutting on the uppermost sheet of the sheet P housed in the feeding cassette 11, and feeds the sheets one by one.

Further, the sheet feeding unit 10 has a manual feed tray 13 as a sheet loading unit capable of loading and supporting the sheet, and feeding rollers 15 and 16 for feeding the sheet supported by the manual feed tray 13. .. The feeding roller 15 as a feeding means rotates while abutting on the top sheet of the sheet supported by the manual feed tray 13 to separate the sheets one by one, and together with the feeding roller 16 as the feeding means, a sheet. Will be sent.

The sheet transfer device 20 as a transfer means includes a transfer roller pair 21, a discharge roller pair 22, and a reverse transfer roller pair 23, 25. The transport roller pair 21 is composed of two rollers that are arranged to face each other and rotate, and a nip portion formed between the two rollers allows the seat to be seated along the seat transport path 2 as the first transport path. Hold and transport. The discharge roller pair 22 and the reverse transfer roller pair 23, 25 will be described later.

The image forming unit 30 as an image forming means includes a photosensitive drum 33, a charging roller 35, a laser scanner 32, a developing roller 36, a transfer roller 37, and a cleaning device 38. In the present embodiment, the photosensitive drum 19, the charging roller 35, the developing roller 36, and the cleaning device 38 are provided as the process cartridge 31 in a detachable manner with respect to the main body of the image forming apparatus 100.

The photosensitive drum 33 as the image carrier rotates counterclockwise in FIG. The charging roller 35 as a charging device uniformly charges (primary charge) the peripheral surface of the photosensitive drum 33 to a predetermined polarity and potential by applying a charging voltage. The laser scanner 32 as an exposure device outputs laser light that is on / off-modulated corresponding to a time-series electric digital pixel signal of image information input from an external device such as an image scanner (not shown) or an external computer. The laser scanner 32 scans while exposing the peripheral surface of the photosensitive drum 33 with this laser beam to eliminate the charge in the exposed bright part of the peripheral surface of the photosensitive drum 33, thereby inputting to the peripheral surface of the photosensitive drum 33. An electrostatic latent image is formed according to the image information.

The developing roller 36 as a developing device is arranged to face the photosensitive drum 33, and by rotating while supporting the toner (developer) on the surface, the toner is supplied to the peripheral surface of the photosensitive drum 33, and the photosensitive drum 33 is supplied. The electrostatic latent image formed on the peripheral surface of the above is sequentially developed as a toner image. In the image forming apparatus 100 of the present embodiment, a reverse developing method is used in which toner is adhered to an exposed bright portion of an electrostatic latent image to develop the image.

The transfer roller 37 as a transfer device is arranged to face the photosensitive drum 33, and is located downstream of the transfer roller pair 21 in the sheet transfer direction (direction A shown in FIG. 1) on the sheet transfer path 2. A transfer nip T is formed between the two. The transfer roller 37 sandwiches and conveys the toner image formed on the peripheral surface of the photosensitive drum 33 by the transfer nip T by applying a transfer voltage having a polarity opposite to that of the toner by a transfer voltage application power supply (not shown). It is electrostatically transferred to the surface of the sheet P. In other words, the transfer roller 37 transfers the toner image on the image carrier to the sheet at the transfer nip T on the first transport path, and forms an unfixed toner image on the sheet. The cleaning device 38 has a cleaning blade 38a, and after the toner image is transferred to the sheet P, residual toner, paper dust, and the like on the peripheral surface of the photosensitive drum 33 are removed by the cleaning blade 38a.

In the present embodiment, the image forming apparatus 100 employs a method of directly transferring the toner image from the photosensitive drum to the sheet, but the present invention is not limited to this, and the toner image formed on the photosensitive member is transferred to the intermediate transfer belt. A method of transferring to a sheet via an intermediate transfer body such as the above may be adopted.

The fixing device 40 as the fixing means is arranged to face the rotating body 42 with the rotating body 42 as the fixing member and the sheet transport path 2 interposed therebetween, and forms a fixing nip F as a nip portion between the rotating body 42 and the rotating body 42. It has a pressurizing roller 41 and a pressurizing roller 41 as a pressurizing member. The fixing nip F is arranged on the sheet transport path 2 downstream of the transfer nip T in the sheet transport direction, and the fixing device 40 heats and pressurizes the sheet sandwiched in the fixing nip F to obtain a toner image. Is fixed to the sheet. Details of the fixing device 40 will be described later.

The discharge roller pair 22 is arranged downstream of the fixing device 40 on the seat transport path 2. The discharge roller pair 22 is composed of two rollers that are arranged to face each other and rotate, and the sheet is sandwiched and conveyed by a nip portion formed between the two rollers to discharge the sheet to the discharge tray 3.

The sheet sensor 80 is located between the transfer roller pair 21 and the transfer nip T on the sheet transfer path 2, that is, downstream of the transfer roller pair 21 in the sheet transfer direction and upstream of the transfer nip T (image forming unit 30). And the media sensor 60 is provided. The sheet sensor 80 is composed of, for example, a transmissive optical sensor or the like, and outputs a detection signal when the optical axis is shielded from light by the sheet conveyed by the transfer roller pair 21.

The media sensor 60 as a detecting means has an output unit (transmitting unit) 61 for outputting sound waves (ultrasonic waves) toward the sheet, and an input unit (receiving unit) 62 for inputting sound waves, and the sheet is conveyed. The output unit 61 and the input unit 62 are arranged so as to sandwich the road 2. The output unit 61 and the input unit 62 of the media sensor 60 have the same configuration, and each has a piezoelectric element (also referred to as a piezo element) which is an interconversion element between mechanical displacement and an electric signal, and an electrode terminal.

In the output unit 61, when a pulse voltage having a predetermined frequency is input to the electrode terminal, the piezoelectric element oscillates to generate a sound wave, and the generated sound wave propagates in the air. When the sound wave reaches the sheet on the sheet transport path 2, the sheet vibrates due to the sound wave. The vibration of the sheet propagates in the air as a sound wave and reaches the input unit 62. In this way, the sound wave generated by the output unit 61 propagates to the input unit 62 via the sheet. The piezoelectric element of the input unit 62 generates an output voltage at the electrode terminal according to the amplitude of the input sound wave. The frequency of the sound wave output by the output unit 61 is preset to an appropriate frequency according to the configuration of the output unit 61 and the input unit 62, the detection accuracy, and the like. In the present embodiment, the output unit 61 outputs an ultrasonic wave having a frequency characteristic of 32 kHz.

With this configuration, the media sensor 60 of the present embodiment detects the basis weight of the sheet conveyed by the transfer roller pair 21. The characteristic of the sheet detected by the media sensor is not limited to the basis weight, and may be, for example, the surface property (surface roughness, glossiness, etc.) of the sheet.

The sheet fed by the sheet feeding unit 10 is detected by the sheet sensor 80 and the media sensor 60 while being conveyed along the sheet conveying path 2 by the conveying roller pair 21, and at the image forming position where the toner image is formed. It is conveyed toward a certain transfer nip T. The sheet is further conveyed while the unfixed toner image is transferred to the surface by the transfer nip T, and is heated and pressed by the fixing nip F, which is the fixing position where the toner image is fixed, to fix the toner image. The sheet on which the toner image is fixed is further conveyed along the sheet transport path 2, and is discharged to the discharge tray 3 by the discharge roller pair 22.

By repeating the above operation, the image forming apparatus 100 forms images on the sheets of the sheet feeding unit 10 one after another. For example, the image forming apparatus 100 can print about 43 black-and-white images per minute on A4 size (210 mm × 297 mm) plain paper at a transport speed of 230 mm / sec. The image forming apparatus is not limited to this, and may be capable of color printing or multicolor printing.

The motor 50 as a driving means simply drives the feeding rollers 12, 15 and 16, each roller pair of the sheet transporting device 20, the photosensitive drum 33, the charging roller 35, the developing roller 36, the transfer roller 37 and the pressure roller 41. It is configured as one motor. Therefore, each part driven by the motor 50 is controlled so as to have a transfer speed with each other. As a result, the image forming apparatus 100 of the present embodiment can reduce the size and cost of the apparatus, and eliminates the need to individually accelerate / decelerate a plurality of motors, thus reducing the processing load on the control unit 70. Can be mitigated.

The image forming apparatus 100 may be configured so that the power from the motor 50 to each part can be connected and disconnected by a clutch mechanism (not shown). Further, the motor for driving the pressurizing roller 41 and the motor for driving the feeding rollers 12, 15, 16 and each roller pair of the sheet transporting device 20 and the photosensitive drum 33 can be independently driven by motors independent of each other. May be.

[Details of fixing device]
Next, the details of the fixing device 40 will be described with reference to FIG. 2. The fixing device 40 includes a rotating body 42, a pressure roller 41, a heater 43 as a heating body, and a thermistor 45 as a temperature detecting means. The rotating body 42 is formed in an endless belt shape (or a cylindrical shape) by, for example, a heat-resistant film having flexibility. The heater 43 is held by the heater holding member 46, and the heater holding member 46 is held by the metal stay member 47. A pressing force is applied between the metal stay member 47 and the pressurizing roller 41 by a pressurizing mechanism (not shown), and the pressurizing roller 41 is pressurized to the heater 43 via the rotating body 42 to rotate. A fixing nip F is formed between the body 42 and the pressure roller 41.

The rotating body 42 is in pressure contact with the pressurizing roller 41, and when the pressurizing roller 41 rotates in the R1 direction shown in FIG. 2 by the rotational driving force of the motor 50, the frictional force with the rotating body 42 at the fixing nip F causes the rotating body 42 to come into contact with the pressurizing roller 41. It rotates in the R2 direction shown in FIG. 2 together with the pressurizing roller 41. The thermistor 45 as a temperature detecting element is arranged so as to be in contact with the heater 43, and outputs a signal corresponding to the temperature of the heater 43. As a result, the image forming apparatus 100 can predict the warming condition (warm-up state) of the fixing apparatus 40 based on the input signal from the thermistor 45. The fixing device 40 is not limited to the one in which the heater 43 comes into direct contact with the rotating body 42, and the heater 43 indirectly touches the rotating body 42 via a sheet material having high thermal conductivity such as iron alloy or aluminum. It may be configured to be in contact with each other.

[Control configuration]
FIG. 3 is a block diagram showing a control configuration of the image forming apparatus 100. The control unit 70 as a control means for controlling each unit of the image forming apparatus 100 includes hardware such as a CPU 71a, a ROM 71b, a RAM 71c, and an I / O 71d. By executing various programs stored in the ROM 71b, the CPU 71a controls the operation of each part of the image forming apparatus 100 related to image formation while using the RAM 71c as a storage means as a working area. Signals from an external device (not shown) connected to the seat sensor 80, the input unit 62 of the media sensor 60, the thermistor 45, and the I / O 71d are input to the control unit 70. The control unit 70 controls the motor 50, the image forming unit 30, the heater 43, and the output unit 61 of the media sensor 60 based on these input signals.

For example, the control unit 70 energizes the heater 43 based on the input signal from the thermistor 45 so that the temperature of the fixing device 40 detected by the thermistor 45, that is, the temperature of the heater 43 becomes the target temperature described later. Control. Further, for example, the control unit 70 operates the motor 50 and the image forming unit 30 based on the input signals (image forming instruction signal, feeding instruction signal) from the external device, and performs an image forming job of forming an image on the sheet. Start.

Further, for example, the control unit 70 detects the tip of the sheet fed by the feeding roller 12 based on the input signal from the seat sensor 80, and electrostatically operates the laser scanner 32 based on the detection timing of the sheet tip. Adjust the timing to start the formation of the latent image. For example, the control unit 70 is an image forming unit so that the tip of the toner image formed on the peripheral surface of the photosensitive drum 33 reaches the transfer nip T at the timing when the tip of the sheet reaches the transfer nip T. 30 is controlled.

Further, the control unit 70 detects the characteristics of the sheet P conveyed by the transfer roller pair 21 based on the input signal from the input unit 62 of the media sensor 60, and in the present embodiment, the basis weight of the sheet P ( (Measure) and store the detection result in the RAM 71c. When the image forming apparatus 100 includes a plurality of seat loading portions capable of loading and supporting the seat as in the present embodiment, the RAM 71c has a sheet detection result (seat characteristics) by the media sensor 60 for each seat loading portion. ) Is memorized. In the present embodiment, the image forming apparatus 100 includes, but is not limited to, two sheet loading portions of the feeding cassette 11 and the manual feed tray 13. For example, the image forming apparatus 100 includes a plurality of feed cassettes, a plurality of manual feed trays, an ADF (Auto Document Feeder), and the like as the sheet loading unit, and the RAM 71c stores the characteristics of the sheet for each of the plurality of sheet loading units. May be good.

Hereinafter, a configuration for detecting the basis weight of the sheet P by the media sensor 60 will be described. The control unit 70 has a basis weight detection control unit 72 that performs input / output control of ultrasonic waves and processing for determining the basis weight of the sheet P (hereinafter referred to as basis weight discrimination process). The control unit 70 controls image formation conditions (fixing conditions) in image formation according to the calculation result of the basis weight detection control unit 72. The image forming conditions refer to, for example, transfer voltage, temperature of the heater 43 of the fixing device 40 (fixing temperature, temperature of the fixing device 40), transfer speed of the sheet, and other conditions for forming an image on the sheet. ..

The CPU 71a of the control unit 70 outputs a signal indicating the start of measurement of the basis weight of the seat P to the drive signal control unit 741 of the basis weight detection control unit 72. When the signal is input from the CPU 71a, the drive signal control unit 741 instructs the drive signal generation unit 731 to generate an ultrasonic output signal in order to generate an ultrasonic wave having a predetermined frequency. The drive signal generation unit 731 can detect only the direct wave output by the output unit 61 by the input unit 62 in order to reduce the influence of disturbance such as reflected waves by the members around the seat P and the sheet transport path 2. , Outputs a pulse wave with a fixed period. This is called a burst wave. In the present embodiment, the drive signal generation unit 731 continuously outputs 5 pulses of a 32 kHz pulse wave in one measurement. In this way, the drive signal generation unit 731 generates a signal having a preset frequency and outputs it to the amplifier 732. The amplifier 732 amplifies the level (voltage value) of the signal having a predetermined frequency input from the drive signal generation unit 731 and outputs it to the output unit 61. In the output unit 61, a piezoelectric element transmits a signal in response to a signal input from the amplifier 732 to generate ultrasonic waves.

The ultrasonic wave output by the output unit 61 or the ultrasonic wave output by the output unit 61 and transmitted through the sheet P is input to the input unit 62, and the signal corresponding to the input ultrasonic wave is transmitted to the basis weight detection control unit 72. Is output to the detection circuit 742 of. The detection circuit 742 has a signal amplification function and a signal rectification function, so that the amplification factor can be changed depending on whether the sheet P does not exist between the output unit 61 and the input unit 62 and the state in which the sheet P exists. I have to. The detection circuit 742 amplifies and rectifies the input signal and outputs it to the AD conversion unit 743. The AD conversion unit 743 converts the signal input from the detection circuit 742 from an analog signal to a digital signal, and outputs the signal to the peak extraction unit 744. The peak extraction unit 744 extracts the peak (maximum value) of the input digital signal based on the digital signal input from the AD conversion unit 743, and stores the extracted peak value in the storage unit 746. These operations are called "peak detection operations".

The peak detection operation is performed a predetermined number of times at predetermined intervals for a state in which the sheet P does not exist and a state in which the sheet P exists between the output unit 61 and the input unit 62. Based on the peak value of the digital signal stored in the storage unit 746, the calculation unit 747 has an average value of a predetermined number of peak values in the absence of the sheet P and a predetermined number of peaks in the presence of the sheet P. The transmission coefficient of ultrasonic waves with respect to the sheet P is calculated from the ratio of the values to the average value. The calculation unit 747 outputs the calculated transmission coefficient to the CPU 71a. The transmission coefficient calculated by the calculation unit 747 is a value having a negative correlation with the basis weight of the sheet P, and the CPU 71a determines the basis weight of the sheet P based on the transmission coefficient calculated by the calculation unit 747.

In the present embodiment, as a means for detecting the characteristics of the sheet, a media sensor that detects the basis weight of the sheet by a sound wave transmitted through the sheet is given as an example, but the present invention is not limited to this. As a means for detecting the characteristics of the sheet, a sensor that detects the characteristics of the sheet by the sound wave reflected by the sheet and input to the input unit may be used. Further, as the characteristics of the sheet, a sensor that detects characteristics other than the basis weight, for example, material, thickness, surface property (surface roughness and glossiness), etc. may be used. Further, a sensor that detects a plurality of characteristics among the characteristics of these sheets may be used.

[Image formation conditions]
Next, the image forming conditions in the image forming job executed by the control unit 70 of the present embodiment will be described. The control unit 70 of the present embodiment discriminates (detects) the basis weight of the sheet based on the detection result (input signal from the media sensor 60) of the media sensor 60, and uses the toner image on the sheet based on the discrimination result. The image formation conditions for fixing (hereinafter referred to as fixing conditions) are determined. For example, the fixing conditions include, among the above-mentioned image forming conditions, the temperature at which the toner image is fixed to the sheet and the transport speed of the sheet when passing through the fixing nip F.

In general, suitable fixing conditions will vary depending on the characteristics of the sheet. For example, fixing a toner image on thick paper having a larger basis weight than plain paper requires a larger amount of heat than fixing a toner image on plain paper. If the amount of heat used to fix the toner image on the sheet is insufficient, the toner image may not be sufficiently fixed on the sheet, causing poor fixing.

For example, in order to give a larger amount of heat to the toner image, a method of raising the temperature of the fixing nip F when fixing the toner image can be considered, but in order to raise the temperature of the fixing nip F, the heater 43 can be considered. The time required to heat the toner increases, and the power consumption increases. Further, for example, in order to give a larger amount of heat to the toner image, the sheet transport speed when passing through the fixing nip (hereinafter referred to as the fixing transport speed) is reduced, and the sheet passes through the fixing nip F. A method of lengthening the time is also conceivable. However, if the fixing transfer speed is reduced, the time required for image formation becomes long.

Therefore, in the present embodiment, the control unit 70 switches the fixing conditions according to the detection result of the media sensor 60 to suppress fixing defects, reduce power consumption, and shorten the time required for image formation. It is possible. For example, when the control unit 70 determines that the sheet on which the image is formed is a sheet having a large basis weight such as thick paper, the control unit 70 switches the temperature of the fixing device 40 so that the temperature of the heater 43 becomes high, or fixes and conveys the sheet. The rotation speed of the motor 50 is switched so that the speed becomes smaller.

Specifically, as shown in Table 1, the control unit 70 of the present embodiment includes the basis weight of the sheet to be conveyed in any of the five ranges based on the detection result of the media sensor 60. To determine. Then, the control unit 70 has a first transfer speed (high speed) in which the sheet fixing transfer speed is 230 mm / sec and a second transfer speed (low speed) in which the sheet fixing transfer speed is 115 mm / sec, depending on the determination result of the basis weight of the sheet. ) And, the transport speed is switched between. For example, the control unit 70 has a first transfer speed when the sheet fixing transfer speed is 60 g / m ² or more and less than 105 g / m ² , and the sheet basis weight is 105 g / m ² or more and 199 g / m. The rotation speed of the motor 50 is controlled so that the second transport speed is obtained when the speed is ² or less.

In the present embodiment, the control unit 70 can switch the sheet transfer speed by the sheet transfer device 20 between the two transfer speeds of the first transfer speed and the second transfer speed. However, it is not limited to this. The control unit 70 may be able to switch the sheet transfer speed by the sheet transfer device 20 between a plurality of three or more transfer speeds, or may be able to continuously change the transfer speed. May be good. Further, in the image forming apparatus 100 of the present embodiment, since the sheet feeding unit 10, the sheet conveying device 20, the image forming unit 30 and the fixing device 40 are driven by a single motor 50, the fixing conveying speed and the fixing transfer speed are increased. , The transport speed of the sheet in other parts is the same.

Further, the control unit 70 controls the fixing device 40 so that the larger the basis weight of the sheet, the higher the fixing temperature within the range of the basis weight of the sheet having the same transfer speed of the sheet. Specifically, the control unit 70 has a sheet tsubo within the range of 60 g / m ² or more and less than 105 g / m ² and 105 g / m ² or more and 199 g / m ² or less. The fixing device 40 is controlled so that the target temperature of the heater 43 becomes higher as the amount is larger. For example, in the control unit 70, when the basis weight of the sheet is 75 g / m ² or more and less than 90 g / m ² , the second value is 60 g / m ² or more and less than 75 g / m ² . The target temperature of the heater 43 is set to a higher temperature than when it is a value.

The control unit 70 is trying to optimize the power consumption and the time required for image formation by switching the target temperature of the heater 43 and the rotation speed of the motor 50 according to the basis weight of the sheet in this way. For example, in the image forming apparatus 100, when an image is formed on a sheet conveyed at a first conveying speed (high speed), the time required to form an image of one A4 size sheet, that is, the first print out time (hereinafter referred to as “first print out time”). , FPOT) is 7.0 sec. Further, for example, in the image forming apparatus 100, the FPOT when forming an image on the sheet conveyed at the second conveying speed (low speed) is 12.0 sec.

[Processing in image formation job]
Next, the processing in the image forming job executed by the control unit 70 of the present embodiment will be described. When transferring the toner image to the sheet in the transfer nip T, it is necessary to adjust the timing so that the toner image formed on the photosensitive drum 33 is transferred to a predetermined position on the sheet. Specifically, after the seat is fed by the seat feeding unit 10, the tip of the seat is detected by the seat sensor 80. Such an image forming apparatus 100 detects (calculates) the timing at which the tip of the sheet reaches the transfer nip T from, for example, the position of the sheet sensor 80 and the position of the transfer nip T, and the transfer speed of the sheet. On the other hand, at the timing when the tip of the sheet reaches the transfer nip T, the exposure for forming an electrostatic latent image on the photosensitive drum 33 so that the tip of the toner image on the photosensitive drum 33 also reaches the transfer nip T. Is done. That is, at the exposure start timing, the length from the tip position of the electrostatic latent image in the circumferential direction of the photosensitive drum 33 to the transfer nip T and the length from the tip of the sheet to the transfer nip T must be the same length. Must be.

For example, if the transport speed is too high or the target temperature is too low when the media sensor 60 detects the basis weight of the sheet, the media sensor 60 detects the basis weight of the sheet in order to suppress fixing defects. Later, a method of changing the sheet transport speed to a smaller value can be considered. However, after the exposure on the photosensitive drum 33 is started, it is not preferable to change the rotation speed of the photosensitive drum 33 in order to prevent the occurrence of the displacement of the electrostatic latent image. Therefore, in the image forming apparatus 100 of the present embodiment in which the transfer of the photosensitive drum 33 and the sheet is driven by a single motor, the transfer speed of the sheet and the rotation speed of the photosensitive drum 33 are changed on the photosensitive drum 33. Must be completed before starting exposure. For that purpose, after the detection of the basis weight (characteristic) of the sheet by the media sensor 60 is completed, the exposure to the photosensitive drum 33 is started at the timing including the time required for changing the speed.

Here, the sheet is conveyed on the sheet transfer path 2 even while the sheet transfer speed is being changed. Therefore, the length along the sheet transport path 2 from the position where the sheet detection by the media sensor 60 ends to the transfer nip T is the length at which the sheet is transported during the speed change and the above-mentioned electrostatic latent image. A length that is the sum of the length from the tip position to the transfer nip T is required. That is, in order to change the sheet transfer speed after the sheet is detected by the media sensor 60, the sheet up to the transfer nip T is changed by the length of the sheet being conveyed while the transfer speed is being changed. It is necessary to lengthen the transport path. Prolonging the sheet transport path leads to an increase in the size of the image forming apparatus.

Therefore, in the present embodiment, the control unit 70 suppresses fixing defects and improves FPOT without changing the transport speed after the sheet is detected by the media sensor 60. Hereinafter, the details of the control in the image forming job by the control unit 70 will be described.

When forming an image on the first sheet in the image forming job, the control unit 70 first drives the fixing device 40 to heat the fixing device 40. After the temperature of the heater 43 reaches the target temperature, the control unit 70 further delays the feeding of the sheet until after the lapse of the delay time tw described later, and then starts feeding the sheet at the first transport speed. The control unit 70 causes the media sensor 60 to detect the characteristics of the sheet while transporting the sheet at the first transport speed (high speed), stores the detection result, that is, the basis weight of the sheet in the RAM 71c, and transports the sheet at the first transport speed. While forming an image on the sheet. When forming an image on the second and subsequent sheets of the sheet, the control unit 70 first drives the fixing device 40 to heat the fixing device 40. After the temperature of the heater 43 reaches the target temperature, the control unit 70 transports the sheet at a transport speed according to the characteristics of the sheet based on the detection result of the first sheet by the media sensor 60 to form an image. I do.

In other words, in the image forming job, the control unit 70 determines whether or not the detection result of the sheet by the media sensor 60 is stored in the RAM 71c when the sheet feeding unit 10 feeds the sheet. Then, the control unit 70 delays the start of feeding when the detection result of the sheet, that is, the characteristics of the sheet is not stored in the RAM 71c, and then transports the sheet at the first transport speed (high speed) to form an image. .. Further, when the characteristics of the sheet are stored, the control unit 70 conveys the sheet at a transfer speed according to the characteristics of the sheet to form an image.

As a result, even when the basis weight of the first sheet of the image forming job is large, the time until the sheet reaches the fixing nip F becomes longer, so that the time for raising the temperature of the fixing nip F is increased. It is possible to secure it, and it is possible to suppress fixing defects. When the detection result of the sheet is not stored in the RAM 71c, the control unit 70 is not limited to the one that transfers the sheet at the first transfer speed (high speed) after delaying the start of feeding to form an image. When the detection result of the sheet is not stored in the RAM 71c, the control unit 70 delays the start of feeding and then transfers the sheet at a predetermined transfer speed faster than the slowest transfer speed (for example, the second transfer speed described above). It suffices if it is configured to carry and form an image.

Hereinafter, with reference to FIG. 4, the details of the processing executed by the control unit 70 in the present embodiment will be described.

As shown in FIG. 4A, when the control unit 70 receives an image formation instruction signal from an external device, an image formation job is started, and the highest-level sheet loaded on the sheet loading unit designated by the received signal. On the other hand, the image forming operation for forming an image is started (S101). When the image forming operation for the sheet is started, the CPU 71a of the control unit 70 determines whether or not the basis weight (characteristic) of the sheet corresponding to the sheet loading unit specified by the image forming instruction signal is stored in the RAM 71c. (S102). For example, when the basis weight of a sheet is not stored in the RAM 71c, it is an image forming operation of an image forming job that forms an image on only one sheet, or an image forming job that continuously forms an image on a plurality of sheets. This is the case of the image forming operation for the first sheet of.

In step S102, when the basis weight of the sheet is not stored in the RAM 71c (NO in S102), the motor 50 is rotated so that the sheet transfer speed becomes the first transfer speed (high speed), and the pressurizing roller 41 The rotation is started (S113). Further, the control unit 70 starts preheating the heater 43 so as to heat up to the initial value of the target temperature (S114). In other words, the control unit 70 detects the first sheet of the image forming job by the media sensor 60 while driving the fixing device 40 before the sheet feeding unit 10 starts feeding the sheets. Regardless of this, the fixing device 40 is heated so as to reach a predetermined fixing temperature. At this time, the control unit 70 heats the fixing device 40 while driving the fixing device 40 at a predetermined transfer speed regardless of the detection result by the media sensor 60. In the present embodiment, the initial value of the target temperature of the heater 43 is 180 ° C., which is a fixing condition for forming an image on the sheet having the smallest basis weight. When the temperature of the heater 43 reaches the target temperature, the control unit 70 starts a feeding delay process for delaying the feeding start of the seat while maintaining the rotation speed of the motor 50 (S115).

The feed delay process is a process of ensuring the preheating time of the fixing device 40 by providing a delay time (standby time) before starting the feed of the sheet in step S105. By warming the fixing device 40 by securing a sufficient preheating time by the feeding delay processing, even if the sheet to be fed is thick paper or the like, when the sheet passes through the fixing nip F at the first transport speed, It is possible to give a sufficient amount of heat to the toner image.

As shown in FIG. 4B, when the feed delay process is started, the control unit 70 first sets the delay reference time t0 (S121). The delay reference time t0 is a time that serves as a reference for the delay time tw, which is the time for delaying the start of feeding, and is determined according to the state of the image forming apparatus 100. For example, the delay reference time t0 is determined according to the temperature of the heater 43 based on the detection temperature of the thermistor 45 at the time when the image forming operation is started (or when the image forming job is started) in step S101.

Specifically, according to Table 2, the control unit 70 sets the delay reference time t0 longer as the temperature of the fixing device 40 is lower, so that a larger preheating time can be secured. For example, when the detection temperature of the thermistor 45 at the time when the image formation operation (image formation job) is started is the first temperature of less than 38 ° C, the detection temperature of the thermistor 45 is the second temperature of 38 ° C or more and less than 55 ° C. The delay reference time t0 is set to be longer than when the temperature is. In other words, the control unit 70 has a second temperature whose difference from the target temperature is smaller than that of the first temperature as compared with the case where the detection result of the thermistor 45 at the start of the image forming job is the first temperature. If so, set the delay time short. The delay reference time t0 is not limited to the one set according to the temperature of the heater 43. For example, a temperature detection device for detecting the temperature inside the main body of the device is separately provided, and the lower the temperature inside the main body of the device, the longer the setting. It may be done.

When the delay reference time t0 is set in the process of step S121, the control unit 70 sets the delay correction value A (S122). The delay correction value A is a correction coefficient for correcting the delay reference time t0 by multiplying the delay reference time t0 when determining the delay time tw. The smaller the delay correction value A, the smaller the delay time tw. In the present embodiment, the delay correction value A is determined according to the image ratio (printing rate) of the image data when forming an image on the sheet. The image ratio is the ratio of the area of the area where the toner image is actually formed to the area of the image forming area of the sheet, and is calculated by the control unit 70 based on the image data input from the external device. For example, when the image ratio is 100%, a toner image is formed over the entire image forming region of the sheet, and when the image ratio is 50%, a toner image is formed in half of the image forming region of the sheet.

In the present embodiment, the control unit 70 sets the delay correction value A smaller as the image has a lower image ratio, so that the delay time tw becomes shorter. For example, the control unit 70 sets the delay correction value A larger when the image ratio is the first ratio of 5% or more than when the image ratio is the second ratio of less than 2%. This is because an image with a large area formed by fine lines or text and a low image ratio can fix a toner image with a smaller amount of heat than an image with a high image ratio such as a photographic image or a solid color image. Because it is. Specifically, the control unit 70 sets the delay correction value A according to Table 3 according to the image ratio of the image data.

Depending on the state of the image forming apparatus 100 and the content of the image data for forming the image, the calculation of the image ratio by the control unit 70 may not be completed at the time of S122. In such a case, the control unit 70 sets the delay correction value A to 1.0 in consideration of the possibility that the image ratio based on the image data is 5% or more.

When the process of step S122 is executed, the control unit 70 sets (calculates) the delay time tw based on the delay reference time t0 and the delay correction value A (S123). In this process, the control unit 70 calculates the product of the delay reference time t0 and the delay correction value A as the delay time tw (tw = t0 × A). In this process, the control unit 70 calculates the delay time tw by multiplying the delay reference time t0 according to the temperature of the heater 43 by the delay correction value A according to the image ratio of the image data, thereby preheating more than necessary. The FPOT is shortened by avoiding securing the time.

When the delay time tw is calculated, the control unit 70 determines the elapsed time from the start of the feed delay process, that is, the elapsed time after the temperature of the heater 43 of the fixing device 40 reaches the target temperature, and the delay time tw. Comparison with (S124). When the elapsed time from the start of the feed delay process is less than the delay time tw (NO in S124), the control unit 70 returns the process to S122.

As described above, at the time of step S122, the calculation of the image ratio by the control unit 70 may not be completed. Therefore, in the process of step S124, if the elapsed time from the start of the feed delay process is less than the delay time tw, the control unit 70 returns the process to step S122 again and sets the value of the delay correction value A. Overwrite the latest value.

On the other hand, in the process of step S124, when the elapsed time from the start of the feed delay process exceeds the delay time tw (YES in S124), the control unit 70 ends the feed delay process. When the feeding delay process is completed, the control unit 70, as shown in FIG. 4A, of the sheet loaded on the sheet loading unit designated by the image formation instruction signal while maintaining the rotation speed of the motor 50. Feeding is started (S105). As described above, for the first sheet of the image forming job, the control unit 70 is a sheet from the time when the fixing device 40 reaches a predetermined fixing temperature (target temperature) until the above-mentioned delay time tw elapses. The start timing of sheet feeding by the feeding unit 10 is delayed.

When the feeding of the seat is started, the control unit 70 determines whether or not the tip of the seat has passed through the seat sensor 80 (S106). When the tip of the sheet does not pass through the sheet sensor 80 (NO in S106), the process is waited (NO in S106), and when the tip of the sheet passes through the sheet sensor 80 (YES in S106), the media discrimination process is executed (S107). In this process, the control unit 70 determines which of the five ranges in Table 1 the basis weight of the fed sheet is included, based on the detection result of the media sensor 60.

When the process of step S107 is executed, the control unit 70 forms an electrostatic latent image on the photosensitive drum 33, forms a toner image on the photosensitive drum 33, transfers the toner image to the sheet, and fixes the toner image on the sheet. The image is formed on the sheet (S108). At this time, the control unit 70 responded to the image forming conditions excluding the sheet transport speed (fixing transport speed) such as the temperature of the heater 43 according to the basis weight of the sheet determined in step S107 while maintaining the sheet transport speed. Image formation is performed by switching to the conditions. For example, the control unit 70 switches the target temperature of the heater 43 to a temperature corresponding to the basis weight of the sheet determined in step S107 according to Table 4.

As a result, for example, even when a sheet having a basis weight of 105 to 199 g / m ² is conveyed at the first transfer rate of 230 mm / sec, the time required for the sheet to reach the fixing nip F becomes longer, so that the temperature of the fixing nip F becomes high. It is possible to secure the time to raise the temperature and suppress the fixing failure. Regarding the fixing conditions when transporting a sheet having a basis weight of 60 to 105 g / m ² , the target temperature of the heater 43 is set from Table 1 in consideration of the fact that the fixing device 40 is warmed by the feed delay process. I'm lowering it.

Further, in the process of step S108, the control unit 70 maintains the sheet transport speed according to the basis weight of the sheet determined in step S107, thereby changing the rotation speed of the photosensitive drum 33 during exposure of the photosensitive drum 33. It prevents the occurrence of displacement of the electrostatic latent image. As described above, the control unit 70 has the first transfer speed when the basis weight of the sheet is not stored in the RAM 71c, that is, for the first sheet of the image forming job, regardless of the detection result by the media sensor 60. An image is formed on the sheet while being conveyed by. When the image forming job is a job for continuously forming an image on a plurality of sheets, the process is returned to step S101, and the image forming operation from step S101 to step S108 is repeated.

In the process for the second and subsequent sheets in the image forming job for continuously forming an image for a plurality of sheets, when the process for step S102 is performed, the sheet is already processed in step S107 for the first sheet. Basis weight is stored in the RAM 71c. In step S102, when the basis weight of the sheet is stored in the RAM 71c (YES in S102), an image is formed on the sheet under the optimum fixing conditions according to the value of the basis weight.

Specifically, the control unit 70 rotates the motor 50 so that the sheet transfer speed becomes the first transfer speed or the second transfer speed slower than the first transfer speed according to the basis weight stored in the RAM 71c. The rotation of the pressurizing roller 41 is started (S103). Further, the control unit 70 starts preheating the heater 43 so as to reach the target temperature according to the basis weight stored in the RAM 71c according to Table 1 (S104). In other words, for the second sheet of the image forming job, the control unit 70 drives the fixing device 40 to perform the first sheet before the sheet feeding unit 10 starts feeding the second sheet. The fixing device 40 is heated so as to have a fixing temperature according to the characteristics. At this time, the control unit 70 heats the fixing device 40 while driving the fixing device 40 at a transport speed corresponding to the characteristics of the first sheet detected by the media sensor 60.

When the temperature of the heater 43 reaches the target temperature, the control unit 70 starts feeding the sheet loaded on the sheet loading unit designated by the image formation instruction signal while maintaining the rotation speed of the motor 50 (S105). ). As described above, for the second sheet of the image forming job, the control unit 70 is the sheet feeding unit 10 when the fixing device 40 reaches the fixing temperature according to the characteristics of the first sheet. We have started to supply seats by.

Since the processing from step S106 to step S108 is the same as the processing for the first sheet, the description thereof will be omitted. In the present embodiment, when the image formation for all the sheets in the image forming job is completed, the control unit 70 sets the sheet transfer speed to the first transfer speed (high speed), sets the target temperature of the heater 43 to 180 ° C., and initially sets the temperature to 180 ° C. To become.

Hereinafter, the difference between the configuration of the present embodiment and the configuration of the prior art will be described. As a comparative example 1 of the prior art, when the characteristics of the sheet are not stored when the image forming operation is started, the second transfer speed (115 mm / sec) regardless of the sheet to be fed is used to suppress the fixing defect. ) Was used to form an image while being conveyed. Other configurations of the image forming apparatus of Comparative Example 1 are the same as those of the present embodiment.

In Comparative Example 1, when the characteristics of the sheet are not stored when the image forming operation is started, the sheet is conveyed at the second transfer speed (low speed) regardless of the sheet to be fed in order to suppress fixing defects. While forming an image. Therefore, in Comparative Example 1, if the characteristics of the sheet are not stored when the image forming operation is started, the FPOT is 12.0 sec regardless of the basis weight of the sheet.

In the present embodiment, for example, when the detection temperature of the thermistor 45 is less than 38 ° C. and the image ratio is 5% or more at the time of S101, the delay reference time t0 is 4.0 sec and the delay correction value A is 1.0. Therefore, the delay time tw is 4.0 × 1.0 = 4.0 sec. Further, as described above, since the FPOT at the first transport speed when the feed delay processing is not performed is 7.0 sec, the FPOT becomes 11.0 sec by adding the delay time tw of 4.0 sec. This is 1.0 sec shorter than the FPOT of Comparative Example 1. Further, when the detection temperature of the thermistor 45 at the time of S101 is 38 ° C. or higher, or when the image ratio is less than 5%, the delay time tw is shorter than 4.0 sec, so that the FPOT is further shortened.

As described above, according to the present embodiment, the transport roller pair 21, the photosensitive drum 33, and the pressure roller 41 can be controlled at the same transport speed. Therefore, the processing load of the control unit 70 can be reduced by controlling the motor 50 with simple control without individually controlling the acceleration / deceleration of the plurality of motors. Further, according to the present embodiment, the control unit 70 determines that the second sheet of the image forming job is based on the image forming conditions according to the characteristics of the first sheet detected by the media sensor 60. Perform image formation. This makes it possible to form an image on the second sheet under the image forming conditions according to the characteristics of the first sheet, and it is possible to suppress fixing defects.

Further, according to the present embodiment, the control unit 70 has a timing at which the sheet feeding unit 10 starts feeding the first sheet of the image forming job rather than starting driving the fixing device 40. To delay. As a result, even when an image is formed on the first sheet whose characteristics are not clear, the time required for the sheet to reach the fixing nip F becomes longer, so that the fixing nip F in the fixing device 40 becomes longer. It is possible to secure the time to raise the temperature of the above and suppress the fixing failure.

Further, according to the present embodiment, the control unit 70 has a timing at which the sheet feeding unit 10 starts feeding the first sheet of the image forming job rather than starting driving the fixing device 40. After delaying, the sheet feeding is started at the first transport speed (high speed). As a result, even when an image is formed on the first sheet whose characteristics are not clear, the sheet feeding is started at the second transport speed (low speed) without delaying the feeding start timing. It is possible to shorten the FPOT and improve the productivity.

Further, according to the present embodiment, the control unit 70 forms an image on the first sheet of the image forming job while conveying the first sheet at a predetermined conveying speed regardless of the characteristics of the sheet. This makes it possible to shorten the sheet transport path as compared with the case where the formation of the electrostatic latent image on the photosensitive drum 33 is started after the sheet characteristics are detected and the transport speed is changed. , The device can be miniaturized.

Further, since the transfer roller pair 21 and the photosensitive drum 33 can be controlled at the same transfer speed, they can be driven by a single motor 50, and the device can be miniaturized and the cost can be suppressed. Further, it is possible to shorten the sheet transfer path as compared with the case where the transfer roller pair 21 and the photosensitive drum 33 are configured to have the same transfer speed and the transfer speed is changed after the sheet is detected by the media sensor. Therefore, the device can be miniaturized.

In the present embodiment, when the image formation for all the sheets in the image forming job is completed, the control unit 70 initializes the sheet transfer speed to the first transfer speed and the target temperature of the heater 43 to 180 ° C. However, it is not limited to this. It suffices if the predetermined transfer speed and the predetermined target temperature are set at the start of the image formation job. For example, the control unit 70 may initialize the sheet transfer speed and the target temperature of the heater 43 at the start of the image formation job. good. Further, the image forming apparatus includes an input device (not shown), and when the user operates the input device at the start of the image forming job, the sheet conveying speed and the target temperature of the heater 43 are set to a predetermined conveying speed and a predetermined target temperature. It may be possible to set so as to be.

Further, in the present embodiment, the control unit 70 is configured to determine the fixing conditions according to the basis weight of the sheet, but the present invention is not limited to this. The control unit 70 may be configured to determine the image formation conditions according to the characteristics of the sheet. For example, the control unit 70 may use the transfer nip T according to the characteristics of the sheet detected by the media sensor 60. It may be configured to determine the transfer voltage of.

The delay reference time t0 may be set according to the installation environment of the image forming apparatus 100. For example, the delay reference time t0 may be set so that the lower the temperature of the installation environment of the image forming apparatus 100, the larger the value. This is because when the installation environment of the image forming apparatus 100 is low temperature, the sheet and toner may also be low temperature, and a larger amount of heat is required to fix the toner image.

Further, in the present embodiment, the delay correction value A is set according to the image ratio of the image data for forming an image on the sheet, but is not limited to this. The delay correction value A may be set, for example, according to the maximum density of the image in a predetermined area of the sheet to be conveyed. In this case, the delay correction value A can be set to be smaller as the maximum density of the image is smaller. For example, when the maximum density of the toner image in the image forming region of the sheet is the first density, the delay correction value A is higher than when the maximum density of the toner image is a second density smaller than the first density. May be set to a large value.

<Second embodiment>
Hereinafter, the second embodiment will be described with reference to FIG. The second embodiment differs from the first embodiment in the processing in the image forming job by the control unit 70. Specifically, the second embodiment is different from the first embodiment in the process of step S102 of the image forming job when the characteristics of the sheet are not stored in the RAM 71c. Other configurations are the same as those of the first embodiment, and the same reference numerals are given to the drawings for the same configurations as those of the first embodiment, and the description thereof will be omitted.

Generally, the rotating body 42 and the pressure roller 41 of the fixing device 40 deteriorate according to the number of rotations. Therefore, in order to improve the durability of the fixing device 40, it is desirable to suppress the rotation speed of the rotating body 42 and the pressure roller 41. Therefore, in the present embodiment, the control unit 70 pressurizes at the second transport speed when the pressurizing roller 41 is rotated to preheat the fixing device 40 when the characteristics of the sheet are not stored in the RAM 71c. The roller 41 is rotated to switch to the first transfer speed before the start of feeding the sheet. As a result, in the present embodiment, the rotation speed of the pressure roller 41 is suppressed and the durability of the fixing device 40 is improved.

Specifically, as shown in FIG. 5A, when the characteristics of the sheet are not stored in the RAM 71c in the process of step S102 (NO in S102), the control unit 70 has a second sheet transfer speed. The rotation of the pressurizing roller 41 is started so as to reach the transport speed (S213). As described above, for the first sheet of the image forming job, the control unit 70 is the first transfer speed at which the image is formed before the sheet feeding unit 10 starts feeding the sheet. The fixing device 40 is driven at a predetermined transfer speed slower than the transfer speed. Then, the control unit 70 of the present embodiment starts preheating of the heater 43 so as to heat up to the initial value of the target temperature (S114), and executes the feeding delay process (S215).

In the present embodiment, the time required to switch the motor rotation speed from the second transport speed (low speed) to the first transport speed (high speed) (motor speed switching time t1) is 1.0 sec. In the present embodiment, when the delay time tw is calculated by the feed delay process, the motor speed switching time t1 is subtracted from the value obtained by multiplying the delay reference time t0 by the delay correction value A, thereby performing the first embodiment. The morphology and FPOT are made to have the same length.

As shown in FIG. 5B, when the feed delay process is started, the control unit 70 sets the delay reference time t0 (S121) and the delay correction value A, as in the first embodiment. Do (S122). When the process of step S122 is executed, the control unit 70 calculates the delay time tw based on the delay reference time t0, the delay correction value A, and the motor speed switching time t1 (S223). In this process, the control unit 70 calculates the delay time tw by subtracting the motor speed switching time t1 from the product of the delay reference time t0 and the delay correction value A (tw = t0 × A−t1).

When the delay time tw is calculated, the control unit 70 compares the elapsed time from the start of the feed delay process with the delay time tw (S124). In the process of step S124, when the elapsed time from the start of the feed delay process exceeds the delay time tw (YES in S124), the control unit 70 ends the feed delay process. When the feeding delay process is completed, the control unit 70 switches the rotation speed of the motor 50 (S216) so that the sheet transport speed becomes the first transport speed (high speed), and is designated by the image formation instruction signal. The feeding of the sheet loaded on the sheet loading unit is started (S105).

As described above, according to the present embodiment, when the pressurizing roller 41 is rotated to preheat the fixing device 40 when the characteristics of the sheet are not stored in the RAM 71c, the pressurization is performed at the second transport speed. The roller 41 is rotated to return to the first transfer speed before the start of feeding the sheet. Thereby, in the present embodiment, the rotation speed of the motor 50 in the state where the sheet is not conveyed can be suppressed, and the durability of the fixing device 40 can be improved while improving the productivity. As a result, the durability of other parts (for example, a transport roller pair, a photosensitive drum, etc.) that are driven by driving the fixing device 40 can also be improved.

<Third embodiment>
Hereinafter, a third embodiment will be described with reference to FIG. The third embodiment differs from the second embodiment in the processing in the image forming job by the control unit 70. Specifically, the third embodiment is different from the second embodiment in the process of step S102 of the image forming job when the characteristics of the sheet are not stored in the RAM 71c. Other configurations are the same as those of the first embodiment, and the same reference numerals are given to the drawings for the same configurations as those of the first embodiment, and the description thereof will be omitted.

In the present embodiment, even if the characteristics of the sheet are not stored in the RAM 71c, it is determined whether to delay the start of feeding depending on the situation, and if the start of feeding is not delayed, the first step is made. 2 An image is formed on the sheet while transporting the sheet at a transport speed (low speed). Specifically, the control unit 70 delays the start of feeding and then forms an image at the first transport speed (high speed), rather than delaying the start of feeding and then forming an image at the second transport speed (low speed). If the FPOT is shorter for the forming, the sheet feeding is started at the second transport speed without delaying the feeding start. This makes it possible to further shorten the FPOT in the present embodiment as compared with the first and second embodiments.

As shown in FIG. 6A, when the preheating of the heater 43 is started so as to heat to the initial value of the target temperature in step S114, the control unit 70 executes the feeding delay and the speed switching process (S315). ..

As shown in FIG. 6B, when the feeding delay and the speed switching process are started, the control unit 70 sets the delay reference time t0 (S121) and the delay correction value A (S122), and delays the time. Calculate tw (S223). In this embodiment, the delay reference time t0 is determined according to Table 5 based on the detection temperature of the thermistor.

When the delay time tw is calculated in the process of step S223, the control unit 70 calculates FPOTtfw (first time) in the case of performing image formation at the first transport speed (high speed) after delaying the start of feeding (first time). S324). In this process, the control unit 70 calculates FPOTtfw by adding FPOTtf1, delay time tw, and motor speed switching time t1 when image formation is performed at the first transfer speed without delaying the transfer start (tfw). = Tf1 + tw + t1). In other words, the control unit 70 sets the delay time tw and obtains the first time required to eject the first sheet when the first sheet is conveyed at the first transfer speed faster than the second transfer speed. ing.

When the process of step S324 is performed, the control unit 70 compares the above-mentioned FPOTfw with FPOTtf2 (second time) in the case where the image is immediately formed at the second transport speed (low speed) without delaying the start of feeding. (S325). In other words, FPOTtf2 is the time required to eject the first sheet when the first sheet is conveyed at the second transfer speed without setting the delay time tw. In the process of step S325, when the FPOTtfw in the case of performing image formation at the first transport speed after delaying the feed start is smaller (NO in S325), the control unit 70 starts the feed delay process. The elapsed time from the above and the delay time tw are compared (S326). In the process of step S326, if the elapsed time from the start of the feed delay process is less than the delay time tw (NO in S326), the control unit 70 returns the process to step S122.

In the process of step S326, when the elapsed time from the start of the feed delay process exceeds the delay time tw (YES in S326), the control unit 70 sets the sheet transfer speed to the first transfer speed. The rotation speed of the motor 50 is switched so as to (S327). When the process of step S327 is executed, the control unit 70 ends the feed delay and speed switching process. When the feeding delay and the speed switching process are completed, the control unit 70 is loaded on the seat loading unit designated by the image formation instruction signal while maintaining the rotation speed of the motor 50 as shown in FIG. 6A. The delivery of the sheet is started (S105).

On the other hand, in the process of step S325, when FPOTtf2 in the case of immediately performing image formation at the second transport speed without delaying the feed start is smaller (YES in S325), the control unit 70 performs the feed delay and speed switching. End the process. When the feeding delay and the speed switching process are completed, the control unit 70 gives an image formation instruction while maintaining the rotation speed of the motor 50 at which the sheet transport speed becomes the second transport speed, as shown in FIG. 6 (A). The feeding of the seat loaded on the seat loading unit designated by the signal is started (S105). As described above, even if the first sheet is used, the control unit 70 delays the start of feeding and then forms an image at the first feeding speed, rather than forming an image at the second feeding speed without delaying the start of feeding. If the FPOT is smaller than that formed, the feed is started at the second transport speed without delaying the start of the feed.

Hereinafter, the difference between the configuration of the third embodiment and the configuration of the second embodiment will be described. For example, consider a case where the detection temperature of the thermistor 45 is less than 38 ° C. and the image ratio is 5% or more at the time of step S101. In this case, according to Table 5, the delay reference time t0 is 6.0 sec. Further, since the image ratio is 5% or more, the delay correction value A is = 1.0, and the motor speed switching time t1 is 1.0 sec. Therefore, the delay time tw is the second and third embodiments. In any of the above, 6.0 × 1.0-1.0 = 5.0 sec. Further, the FPOTtf1 in the case of performing image formation at the first transport speed without delaying the start of transport is 7.0 sec as described above. Therefore, under this condition, the FPOTtfw when the image formation is performed at the first transfer speed after the transfer start is delayed is tf1 + tw + t1 = 7.0 + 5.0 + 1.0 = 13.0 sec.

Further, the FPOTtf2 in the case of performing image formation at the second transport speed without delaying the transport start is 12.0 sec as described above, and the image is imaged at the first transport speed after the transport start is delayed under this condition. It is shorter than FPOTtfw when forming. Therefore, under this condition, the FPOT in the second and third embodiments is 12.0 sec, and there is no difference in the FPOT.

Further, for example, consider the case where the detection temperature of the thermistor 45 is less than 38 ° C. and the image ratio is less than 2% at the time of S101. In this case, similarly, according to Table 5, the delay reference time t0 is 6.0 sec. Further, since the image ratio is less than 2%, the delay correction value A is = 0.6, and the motor speed switching time t1 is 1.0 sec. Therefore, the delay time tw is the second and third embodiments. In any of the above, 6.0 × 0.6-1.0 = 2.6 sec. Similarly, the FPOTtf1 in the case of performing image formation at the first transport speed without delaying the start of transport is 7.0 sec. Therefore, under this condition, the FPOTtfw when the image formation is performed at the first transfer speed after the transfer start is delayed is tf1 + tw + t1 = 7.0 + 2.6 + 1.0 = 10.6 sec.

Further, the FPOTtf2 in the case of performing image formation at the second transport speed without delaying the start of transport is also 12.0 sec. Therefore, under this condition, the FPOT in the second embodiment is 12.0 sec, and the FPOT in the third embodiment is 10.6 sec. Therefore, under this condition, the FPOT of the third embodiment is 1.4 sec shorter than the FPOT of the second embodiment. Further, in the third embodiment, since the image is formed while the sheet is conveyed at the second conveying speed (low speed), it is possible to suppress fixing defects.

As described above, according to the present embodiment, the image formation is performed at the second transport speed without delaying the feed start rather than the image formation at the first transport speed after the feed start is delayed. If the FPOT is shorter, the sheet feeding is started at the second transport speed without delaying the feeding start. As a result, in the present embodiment, the FPOT can be further shortened as compared with the first and second embodiments, and the fixing failure can be suppressed while improving the productivity.

10 ... Transport means (sheet feeding unit) / 20 ... Transport means (sheet transport device) / 30 ... Image forming means (image forming unit) / 40 ... Fixing means (fixing device) / 45 ... Temperature detecting means (thermistor) / 50 ... Motor / 60 ... Detection means (media sensor) / 61 ... Output unit / 62 ... Input unit / 70 ... Control means (control unit) / 100 ... Image forming device / tw ... Delay time / P ... Sheet

Claims (11)

The means of transporting the sheet and
An image forming means for forming an unfixed toner image on a sheet conveyed by the conveying means, and an image forming means.
A fixing means for fixing the toner image formed by the image forming means to the sheet by heating and pressurizing the sheet.
A detecting means for detecting the characteristics of the sheet conveyed by the conveying means, and
A control means for switching the sheet transfer speed by the transfer means between a first transfer speed and a plurality of transfer speeds including a second transfer speed slower than the first transfer speed according to the detection result of the detection means. , Equipped with
The control means is
For the second sheet of the image forming job, the transport means is controlled so that the second sheet is transported at a transport speed according to the characteristics of the first sheet detected by the detection means.
The first sheet of the image forming job is conveyed at a predetermined transfer speed faster than the second transfer speed after a delay time elapses after the fixing means reaches the target temperature. Control the transport means,
An image forming apparatus characterized in that. The control means is
The temperature of the fixing means can be switched according to the detection result of the detection means.
For the second sheet of the image forming job, the target temperature of the fixing means before the start of transporting the sheets by the transporting means is set according to the characteristics of the first sheet detected by the detecting means. Set to the same temperature
For the first sheet of the image forming job, the target temperature of the fixing means before the start of transporting the sheets by the transporting means is set to a predetermined temperature regardless of the detection result by the detecting means.
The image forming apparatus according to claim 1. A temperature detecting means for detecting at least one of the temperature of the fixing means and the temperature inside the main body of the apparatus is provided.
The control means has a second temperature whose difference from the target temperature is smaller than that of the first temperature as compared with the case where the detection result of the temperature detecting means at the start of the image forming job is the first temperature. In the case of temperature, the delay time is set short.
The image forming apparatus according to claim 1 or 2. The control means sets the delay time, and when the first sheet is conveyed at a predetermined transfer speed faster than the second transfer speed, the first time required to eject the sheet and the said. When the first sheet is transported at the second transport speed without setting a delay time, the second time required for the sheets to be ejected is compared with the second time, which is higher than the first time. When 2 hours is shorter, the transport means is controlled so that the sheet is transported at the second transport speed without setting the delay time even for the first sheet.
The image forming apparatus according to any one of claims 1 to 3. A single motor for driving the transport means and the image forming means.
The image forming apparatus according to any one of claims 1 to 4. The motor drives the fixing means and
For the first sheet of the image forming job, the control means drives the fixing means at a transport speed slower than the predetermined transport speed before the start of feeding the sheets by the transport means. The fixing means is heated, and then the motor is controlled so that the transfer means conveys the sheet at the predetermined transfer speed.
The image forming apparatus according to claim 5. In the control means, for the first sheet of the image forming job, the image ratio when forming an image on the sheet is smaller than the first ratio as compared with the case of the first ratio. In the case of the ratio of, the delay time is set short.
The image forming apparatus according to any one of claims 1 to 6. In the control means, for the first sheet of the image forming job, the maximum density at the time of forming an image on the sheet is smaller than the first density as compared with the case of the first density. When the concentration is 2, the delay time is set short.
The image forming apparatus according to any one of claims 1 to 6. The detection means is arranged upstream of the image forming means in the sheet transport direction.
The image forming apparatus according to any one of claims 1 to 8. The detection means detects the basis weight as a characteristic of the seat, and
In the control means, when the basis weight of the sheet conveyed by the transfer means is the first value, the temperature of the fixing means is higher than when the basis weight is a second value smaller than the first value. The temperature of the fixing means is switched according to the basis weight of the sheet detected by the detecting means so that the temperature becomes high.
The image forming apparatus according to any one of claims 1 to 9. The detection means has an output unit that outputs sound waves toward a sheet and an input unit that inputs sound waves.
The image forming apparatus according to any one of claims 1 to 10.

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