JP2023161247A - Image forming apparatus - Google Patents

Abstract

To prevent the occurrence of printing failure when performing printing on a non-slippery medium.SOLUTION: An image forming apparatus 1 comprises: photoreceptor drums (image carriers) 21 that each carry a toner image (developer image); a conveying belt (conveying unit) 31 that conveys a medium P to which the toner images are transferred from the photoreceptor drums 21; and a print control unit (control unit) 100 as a control unit that detects the physical quantity corresponding to the non-slipperiness of the medium P, and changes a conveying force or a conveying speed of the conveying belt 31 according to the detected physical quantity.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to an image forming apparatus that forms an image on a medium.

In an image forming apparatus using electrophotography, a developer image formed on the surface of a photoreceptor drum serving as an image carrier is transferred to a medium to be transported. In order to improve printing quality, a predetermined speed difference is set between the circumferential speed of the photoreceptor drum and the conveyance speed of the medium. It has also been proposed to increase the speed difference in a high-temperature, high-humidity environment and to decrease the speed difference in a low-temperature, low-humidity environment (see Patent Document 1).

Japanese Patent Application Publication No. 2003-295729 (see abstract)

On the other hand, when a non-slip medium is used, if a speed difference is provided between the circumferential speed of the photoreceptor drum and the transport speed of the medium, the speed difference will accumulate as the printing operation progresses, and the transport motor will Step-out may occur and print defects such as horizontal stripes may occur.

The present disclosure aims to suppress the occurrence of printing defects.

The image forming apparatus of the present disclosure includes an image carrier that carries a developer image, a transport unit that transports a medium to which the developer image is transferred from the image carrier, and a physical quantity that corresponds to the slipperiness of the medium. , and a control section that switches the conveyance force or conveyance speed of the conveyance section according to the detected physical quantity.

According to the present disclosure, since the conveyance force or conveyance speed of the conveyance section is switched based on a physical quantity corresponding to the slipperiness of the medium, printing defects can be suppressed.

1 is a diagram showing the basic configuration of an image forming apparatus according to a first embodiment; FIG. 1 is a block diagram showing a control system of an image forming apparatus according to a first embodiment; FIG. FIG. 3 is a schematic diagram showing the state of occurrence of horizontal stripes according to the first embodiment. 3 is a flowchart showing a printing operation of the image forming apparatus according to the first embodiment. 7 is a flowchart showing the printing operation of the image forming apparatus according to the second embodiment. FIG. 3 is a schematic diagram showing an example of a print mode selection screen. FIG. 3 is a diagram showing the basic configuration of an image forming apparatus according to a third embodiment.

Embodiment 1.
<Configuration of image forming apparatus>
FIG. 1 is a diagram showing the basic configuration of an image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 forms an image using electrophotography, and is a printer here. The image forming apparatus 1 includes a medium supply section 10 that supplies a medium P such as printing paper, image forming units 20K, 20Y, 20M, and 20C that form a toner image on the medium P, and a transfer unit that transfers the toner image onto the medium P. It has a unit 30, a fixing unit 40 that fixes a toner image on the medium P, a medium discharge section 50 that discharges the medium P, and a casing 70 that houses these.

The medium supply unit 10 includes a medium cassette 11 as a medium storage unit, a paper feed roller 12 as a paper feed unit, a separation pad 13 as a contact member, a conveyance roller 14, and a pinch roller 15.

The medium cassette 11 accommodates the medium P and is detachably attached to the casing 70 of the image forming apparatus 1 . The medium cassette 11 includes a mounting plate on which the medium P is placed, and a guide 11a that defines the position of the medium P. The paper feed roller 12 is rotated by a paper feed motor 16 (FIG. 2), and feeds the medium P one by one from the medium cassette 11 to the conveyance path A1.

The separation pad 13 is a pad made of rubber, for example, and applies frictional force by contacting the medium P sent out by the paper feed roller 12, thereby preventing double feeding of the medium P. The conveyance roller 14 is rotated by a paper feed motor 16 (FIG. 2) and further conveys the medium P sent out to the conveyance path A1. The pinch roller 15 is a driven roller pressed by the conveyance roller 14.

The image forming units 20K, 20Y, 20M, and 20C are arranged in this order along the conveyance path of the medium P. The image forming units 20K, 20Y, 20M, and 20C form toner images (developer images) using black, yellow, magenta, and cyan toners (developer).

The image forming units 20K, 20Y, 20M, and 20C include photoreceptor drums 21K, 21Y, 21M, and 21C as image carriers, charging rollers 22K, 22Y, 22M, and 22C as charging members, and developer carriers. It has developing rollers 24K, 24Y, 24M, and 24C, supply rollers 25K, 25Y, 25M, and 25C as supply members, and toner cartridges 26K, 26Y, 26M, and 26C as developer storage bodies. Furthermore, exposure heads 23K, 23Y, 23M, and 23C as exposure devices are arranged so as to face the photoreceptor drums 21K, 21Y, 21M, and 21C.

Since the image forming units 20K, 20Y, 20M, and 20C have the same configuration in common except for toner, they will be referred to as image forming units 20 unless there is a need to distinguish them.

Similarly, the charging rollers 22K, 22Y, 22M, and 22C are referred to as the charging roller 22, the exposure heads 23K, 23Y, 23M, and 23C are referred to as the exposure head 23, and the developing rollers 24K, 24Y, 24M, and 24C are referred to as the developing roller 24. , supply rollers 25K, 25Y, 25M, and 25C are referred to as supply rollers 25, and toner cartridges 26K, 26Y, 26M, and 26C are referred to as toner cartridges 26.

The photosensitive drum 21 is a cylindrical member having a photosensitive layer formed on the surface of a conductive support. The photosensitive layer is a laminate of a charge generation layer and a charge transport layer. The photosensitive drum 21 is rotated clockwise in the figure by a drum motor 27 (FIG. 2).

The charging roller 22 is arranged so as to be in contact with the surface of the photoreceptor drum 21 and rotates following the photoreceptor drum 21 . A charging voltage is applied to the charging roller 22, and the surface of the photoreceptor drum 21 is uniformly charged.

The exposure head 23 includes an LED array in which LEDs (light emitting diodes) as light emitting elements are arranged, and a lens array. The exposure head 23 irradiates the surface of the photoreceptor drum 21 with light to form an electrostatic latent image. The exposure head 23 is suspended and supported by a top cover 71 that covers the upper part of the housing 70.

The developing roller 24 is arranged so as to be in contact with the surface of the photoreceptor drum 21, and rotates in a direction opposite to that of the photoreceptor drum 21 (a direction in which the direction of movement of the surface at the contact portion is the forward direction). A developing voltage is applied to the developing roller 24, and the electrostatic latent image on the photosensitive drum 21 is developed with toner.

The supply roller 25 is arranged so as to be in contact with the surface of the developing roller 24, and rotates in the same direction as the developing roller 24 (in the direction in which the direction of movement of the surface at the contact portion is opposite). The supply roller 25 is applied with a supply voltage and supplies toner to the developing roller 24 .

The toner cartridge 26 is a removable container that stores toner as a developer, and supplies the toner to the developing roller 24 and the supply roller 25 .

The transfer unit 30 includes a conveyance belt 31 as a conveyance section in contact with the photoreceptor drums 21K, 21Y, 21M, and 21C, a drive roller 32 and a tension roller 33 as drive sections around which the conveyance belt 31 is stretched, and the conveyance belt 31. It has a transfer roller 34 as a transfer member that is pressed against the photoreceptor drums 21K, 21Y, 21M, and 21C via.

The conveyance belt 31 attracts and holds the medium P and conveys it along the photoreceptor drums 21K, 21Y, 21M, and 21C. The drive roller 32 is rotated by a belt motor 35 (FIG. 2) and causes the conveyor belt 31 to travel. Tension roller 33 applies a constant tension to conveyor belt 31 . Transfer roller 34 is applied with a transfer voltage and transfers the toner image on the surface of photoreceptor drum 21 to medium P on conveyor belt 31 .

The fixing unit 40 is arranged downstream of the image forming unit 20 in the conveyance direction of the medium P. The fixing unit 40 includes a fixing roller 41 and a pressure roller 42.

The fixing roller 41 has a built-in heater 43 (FIG. 2) such as a halogen lamp, and is heated to a surface temperature of 200° C., for example. The pressure roller 42 is pressed against the fixing roller 41 to form a fixing nip. The fixing roller 41 is rotated by a fixing motor 44 (FIG. 2) and conveys the medium P. The fixing roller 41 and the pressure roller 42 fix the toner image on the medium P by heating and pressing the medium P.

The medium discharge section 50 includes a discharge roller 51 and a pinch roller 52 on the conveyance path A2 from the fixing unit 40 to the discharge port. The ejection roller 51 rotates by rotation transmission from the fixing motor 44 (FIG. 2) and ejects the medium P from the ejection port. The pinch roller 52 is pressed against the discharge roller 51. The top cover 71 is formed with a stacker section 53 on which the medium P discharged from the discharge port is placed.

A paper feed sensor 61 is arranged downstream of the paper feed roller 12 along the conveyance path of the medium P in the image forming apparatus 1 . Further, an entrance sensor 62 is arranged on the upstream side of the conveyance roller 14, and a write sensor 63 is arranged on the downstream side. Further, a slack sensor 64 is arranged on the upstream side of the fixing unit 40, and a discharge sensor 65 is arranged on the downstream side of the fixing unit 40.

The paper feed sensor 61, the entrance sensor 62, the write sensor 63, the slack sensor 64, and the discharge sensor 65 are all sensors that detect passage of the medium P. These sensors 61 to 65 output an ON signal when the leading edge of the medium P passes, and output an OFF signal when the trailing edge of the medium P passes. The sensors 61 to 64 may be mechanical sensors having retractable levers that come into contact with the medium P, or may be optical sensors that optically detect the medium P.

A detection signal from the paper feed sensor 61 is used to determine whether or not the medium P is supplied from the medium cassette 11 to the transport path A1.

A detection signal from the entrance sensor 62 is used to determine the rotation start timing of the conveyance roller 14. Furthermore, the detection signal from the entrance sensor 62 is also used to measure time T1, which will be described later. The entrance sensor 62, together with the CPU 101, corresponds to a detection unit that detects a physical quantity (here, time T1) corresponding to the slipperiness of the medium P.

A detection signal from the write sensor 63 is used to determine the exposure start timing of the exposure head 23. Furthermore, the detection signal from the write sensor 63 is also used to measure the length L of the medium P, which will be described later. The write sensor 63 corresponds to a length measuring section that measures the length L of the medium P together with the CPU 101.

A detection signal from the slack sensor 64 is used to finely adjust the rotational speed of the fixing roller 41. A detection signal from the discharge sensor 65 is used to detect a conveyance failure (jam detection) such as wrapping of the medium P around the fixing roller 41.

Note that, in consideration of the fact that the circumferential speed of the fixing roller 41 changes due to a change in the temperature of the outer diameter of the fixing roller 41, the image forming apparatus 1 is designed so that the medium P is loosened by a predetermined amount between the conveyor belt 31 and the fixing roller 41. It is configured. If the amount of slack is small, the image on the medium P will be misaligned, and if the amount of slack is large, the medium P will come into contact with the surroundings. Therefore, the rotation speed of the fixing roller 41 is finely adjusted based on the detection signal of the slack sensor 64. There is. A detailed explanation of this point will be omitted.

Although not shown in FIG. 1, the image forming apparatus 1 includes rollers arranged at intervals equal to or less than the minimum medium length along the conveyance path of the medium P, motors for rotating these rollers, and power. It further includes a clutch or the like for switching transmission.

Although the image forming apparatus 1 described here is configured to form a color image using the image forming units 20K, 20Y, 20M, and 20C, the configuration is not limited to this. For example, a monochrome image may be formed using a single image forming unit.

<Control system of image forming apparatus>
FIG. 2 is a block diagram showing a control system of the image forming apparatus 1. As shown in FIG. The image forming apparatus 1 includes a print control section 100 as a control section (control circuit), an I/F (interface) control section 110, a reception memory 111, and an image data editing memory 112. The I/F control section 110, reception memory 111, and image data editing memory 112 may be provided separately from the print control section 100, or may be incorporated into the print control section 100.

The I/F control unit 110 controls transmission and reception of print data and the like with a host device. The reception memory 111 temporarily stores print data input via the I/F control unit 110. The image data editing memory 112 records image data formed by editing the print data stored in the receiving memory 111.

The print control unit 100 includes a CPU 101 as a main control unit, an exposure control unit 102, a temperature adjustment circuit 103 as a fixing control unit, a motor driver 104 as a paper feed control unit, and a motor driver 105 as a transport control unit. It has a flash ROM 106 and an EEPROM 107 as storage units.

The exposure control unit 102 controls the light emission of each LED of the exposure head 23 based on the print data stored in the image data editing memory 112. The temperature adjustment circuit 103 controls the heater 43 based on a detection signal from a temperature sensor (not shown) provided in the fixing unit 40 .

The motor driver 104 controls a paper feed motor 16 that rotates the paper feed roller 12 of the medium supply unit 10 . The paper feed motor 16 is, for example, a stepping motor.

The motor driver 105 controls a belt motor 36 that rotates the drive roller 32 of the transfer unit 30 . The belt motor 36 is, for example, a stepping motor.

Flash ROM 106 stores operating programs for image forming apparatus 1 . The EEPROM 107 stores the number of printed sheets and various parameters necessary for color misregistration correction and density correction, and is rewritten whenever there is a change in these parameters.

The image forming apparatus 1 also includes a high-voltage power supply unit 114 that applies a charging voltage, a developing voltage, a supply voltage, and a transfer voltage to the charging roller 22, the developing roller 24, the supply roller 25, and the transfer roller 34, respectively.

The image forming apparatus 1 also includes an operation panel 113 on which a user performs operation input. The operation panel 113 has a display section and an operation section, and is, for example, a touch panel.

The CPU 101 of the print control unit 100 also receives detection signals from the paper feed sensor 61, entrance sensor 62, write sensor 63, slack sensor 64, and discharge sensor 65 described with reference to FIG. 1, as well as a density sensor (not shown). Detection signals from the temperature and humidity sensor are also input.

Based on the input information, the CPU 101 sends control signals to the high voltage power supply section 114, the exposure control section 102, the temperature adjustment circuit 103, the drum motor 27, the fixing motor 44, and the motor drivers 104 and 105.

Note that the drum motor 27 that rotates the photosensitive drum 21 is, for example, a brushless DC motor. Although only one drum motor 27 is shown in FIG. 2, four drum motors 27 are actually provided corresponding to the photosensitive drums 21K, 21Y, 21M, and 21C.

The fixing motor 44 that rotates the fixing roller 41 is, for example, a brushless DC motor. Both the drum motor 27 and the fixing motor 44 are constructed integrally with a board in which a motor driver is incorporated. However, the motor drivers for the drum motor 27 and the fixing motor 44 may be incorporated into the print control section 100.

<Countermeasures against printing defects>
Next, countermeasures against printing defects in the first embodiment will be explained. In the image forming apparatus 1, the medium P supplied from the medium supply section 10 is attracted and held by the conveyor belt 31, and is conveyed along the image forming units 20K, 20Y, 20M, and 20C.

In each image forming unit 20, a charging roller 22 uniformly charges the surface of the photoreceptor drum 21. The surface of the photoreceptor drum 21 is exposed by the exposure head 23 to form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 21 is developed with toner on the developing roller 24 to form a toner image. The toner image on the photosensitive drum 21 is transferred to the medium P conveyed by the conveyor belt 31.

The medium P to which the toner images of the image forming units 20K, 20Y, 20M, and 20C have been transferred is conveyed to the fixing unit 40, heated and pressed by the fixing roller 41 and the pressure roller 42, and the toner image is transferred to the medium P. It will be established.

Generally, each roller (including the photosensitive drum 21) of the image forming unit 20 and the transfer unit 30 is manufactured with a tolerance of about 0.1%. If the conveyor belt 31 becomes slack and the length of the conveyor belt 31 between the transfer sections becomes longer, the transfer positions of the toner images of each color may shift, resulting in changes in color tone and blurring of outlines.

Therefore, for the purpose of improving printing quality, a predetermined speed difference is set between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21. In this embodiment, the running speed of the conveyor belt 31 is set to be 0 to 1% (for example, 0.5%) faster than the circumferential speed of the photoreceptor drum 21.

The running speed of the conveyor belt 31 refers to the moving speed ([mm/sec]) of the surface of the conveyor belt 31 when passing through the image forming units 20K, 20Y, 20M, and 20C. The circumferential speed of the photoreceptor drum 21 refers to the moving speed ([mm/sec]) of the surface of the photoreceptor drum 21, that is, the outer peripheral surface.

Since the medium P is conveyed while being attracted to the conveyor belt 31, no slippage occurs between the medium P and the conveyor belt 31, but slippage occurs between the medium P and the surface of the photoreceptor drum 21. On the other hand, the medium P includes a slippery medium (for example, plain paper) and a non-slippery medium (for example, matte paper) depending on the coefficient of friction of its surface. When printing on a non-slippery medium P, as the conveyance of the medium P progresses, a speed difference accumulates, the load on the belt motor 36 increases, and there is a possibility that step-out occurs.

FIG. 3 is a diagram showing an example of a printed image on the medium P. Here, band-shaped images 8K, 8Y, 8M, and 8C of black, yellow, magenta, and cyan are formed from one side (left side in the figure) to the other side (right side in the figure) in the width direction of the medium P. There is. Each image is a halftone image with a duty ratio of 25%.

As shown in FIG. 3, when the belt motor 36 loses synchronization, horizontal stripes 9 are formed in the print image 8 in a direction perpendicular to the conveying direction. For example, the horizontal streaks 9M of the magenta image 8M and the horizontal streaks 9C of the cyan image 8C occur at the same timing, and the distance D between these two horizontal streaks 9M and 9C is determined by the transfer area of the photoreceptor drums 21M and 21C. is the same as the interval. Note that the horizontal streaks 9K of the black image 8K occur at a timing earlier than the horizontal streaks 9M and 9C.

In this embodiment, when printing on a non-slippery medium P, the drive current of the belt motor 36 is increased compared to when printing on a slippery medium P, and the torque is increased to cope with the load. . The increase width of the drive current is, for example, 25%.

<Printing operation of image forming apparatus>
Next, the printing operation of the image forming apparatus 1 will be explained with reference to FIG. 4. FIG. 4 is a flowchart showing the printing operation of the image forming apparatus 1. When the CPU 101 receives a print command and print data from the host device via the I/F control unit 110, it starts a printing operation.

First, the CPU 101 starts heating the heater 43, and starts rotating the drum motor 27, belt motor 35, and fixing motor 44 (step S101). This increases the surface temperature of the fixing roller 41, causing the photosensitive drum 21, the fixing roller 41, and the drive roller 32 to rotate. As the photosensitive drum 21 rotates, the charging roller 22, the developing roller 24, and the supply roller 25 also rotate.

Further, in step S101, a charging voltage, a developing voltage, and a supply voltage are applied from the high-voltage power supply section 114 to the charging roller 22, developing roller 24, and supplying roller 25 of each image forming unit 20, respectively. The surface of the photosensitive drum 21 is uniformly charged by the charging voltage of the charging roller 22.

Further, the CPU 101 temporarily records print data received from the host device in the reception memory 111 , edits the recorded print data to generate image data, and records the image data in the image data editing memory 112 .

When the temperature of the heater 43 is stabilized and the rotation of each motor 27, 35, 44 is stabilized, the CPU 101 rotates the paper feed motor 16 and also operates a clutch (not shown) to rotate the paper feed roller 12 (step S102). . As the paper feed roller 12 rotates, the medium P in the medium cassette 11 is sent out to the conveyance path A1 while contacting the separation pad 13. When the paper feed sensor 61 detects the leading edge of the medium P, the CPU 101 detects that paper feeding has been performed normally.

When the entrance sensor 62 detects the leading edge of the medium P (step S103), the CPU 101 operates a clutch (not shown) at a predetermined timing to rotate the conveyance roller 14. The conveyance roller 14 and the pinch roller 15 correct the skew of the medium P and convey it toward the conveyance belt 31 .

Next, the CPU 101 determines whether or not the first sheet is fed after the medium cassette 11 is installed (step S104). Since the CPU 101 stores information such as the exchange history of the medium cassette 11, it can determine whether or not the first sheet is being fed after the medium cassette 11 is installed based on this stored information.

Next, the CPU 101 calculates the time (referred to as time T1) from the start of rotation of the paper feed roller 12 until the entrance sensor 62 detects the leading edge of the medium P, and determines whether the time T1 is longer than the specified value Th. It is determined whether or not (step S105).

The less slippery the medium P is, the greater the frictional resistance during conveyance, so the time T1 until it reaches the entrance sensor 62 tends to be longer. The specified value Th is a value obtained by adding 10 msec to the standard time Ts required for standard size plain paper (a typical example of a slippery medium) to reach the entrance sensor 62 from the paper feed roller 12. If the time T1 is longer than the specified value Th, it is treated as a non-slippery medium P, and if the time T1 is less than the specified value Th, it is treated as a slippery medium P.

If the time T1 is longer than the specified value Th (YES in step S105), the CPU 101 turns on the current up flag (step S106).

Further, when the current up flag is ON, the CPU 101 increases the driving current of the belt motor 35 from the motor driver 105 by, for example, 25% higher than when the current up flag is OFF (step S107).

That is, when printing on a non-slippery medium P, the drive current of the belt motor 35 is increased compared to when printing on a slippery medium P, and the torque of the belt motor 35 (that is, the driving force of the conveyor belt 31) is increased. increase.

By increasing the torque of the belt motor 35 in this way, even if the load on the belt motor 35 increases due to the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21, the belt motor 35 will not step out. rotation can be continued without

Note that if the time T1 is less than or equal to the specified value Th (NO in step S105), since the medium P is slippery, step S106 is skipped.

When the medium P is further conveyed and the write sensor 63 detects the leading edge of the medium P, the exposure heads 23K, 23Y, 23M, and 23C are driven at predetermined timings (step S107). As a result, latent images are formed on the surfaces of the photoreceptor drums 21K, 21Y, 21M, and 21C. The latent images on the photoreceptor drums 21K, 21Y, 21M, and 21C are developed with toner from developing rollers 24K, 24Y, 24M, and 24C.

Furthermore, after a predetermined period of time has elapsed from the start of exposure of each of the exposure heads 23K, 23Y, 23M, and 23C, a transfer voltage is applied to the transfer roller 34 facing them (step S108). As a result, the toner images on the photoreceptor drums 21K, 21Y, 21M, and 21C are sequentially transferred to the medium P on the conveyor belt 31.

When the rear end of the medium P passes the write sensor 63 (YES in step S111), the CPU 101 calculates the length L of the medium P (step S112). The length L of the medium P can be calculated from the difference between the time when the leading edge of the medium P passes the write sensor 63 and the time when the rear end of the medium P passes the write sensor 63.

When the calculated length L of the medium P is within the range (specified range) of A-3 [mm]≦L≦A-1 [mm] with respect to the standard length A based on the standard size of the medium P. (YES in step S113), the current up flag is turned off (step S114). The reference length A is set by the CPU 101 based on the size of the medium P (usually a standard size) specified by the print command.

If the length of the medium P is shorter than the standard size, there is a possibility that the medium P in the medium cassette 11 is placed further back than the paper feed roller 12 (on the left side in FIG. 1). In this case, the reason why the time T1 until the medium P reaches the entrance sensor 62 is longer is considered to be not the slipperiness of the medium P but the misalignment of the medium P in the medium cassette 11. Therefore, if the length L of the medium P is within the above specified range, the current up flag that was set to ON in step S106 is returned to OFF.

However, if the length L of the medium P is less than A-3 [mm], it is assumed that the user has aligned the guide 11a in the medium cassette 11 so that a paper feeding error does not occur. Therefore, the current up flag is maintained as is.

Further, if the calculated length L of the medium P is outside the above specified range (NO in step S113), the current up flag is maintained as it is.

Note that at the time when steps S112 to S114 are performed, the transfer of the toner image to the medium P has already progressed, so the drive current of the belt motor 35 based on the result of step S114 is changed to the next medium P. Applies from the time of printing.

The conveyor belt 31 to which the toner images on the photoreceptor drums 21K, 21Y, 21M, and 21C have been transferred is conveyed to the fixing unit 40 by the conveyor belt 31. In the fixing unit 40, a fixing roller 41 and a pressure roller 42 apply heat and pressure to the medium P to fix the toner image on the medium P.

The medium P on which the toner image is fixed is sent to the medium discharge section 50 by the rotation of the fixing roller 41. In the medium discharge section 50, the discharge roller 51 conveys the medium P along the conveyance path A2 and discharges it from the discharge port. The ejected medium P is stacked on the stacker section 53.

When a predetermined time has elapsed since the rear end of the medium P passed the write sensor 63 in step S111, the transfer voltage of the transfer roller 34 is turned off (step S115).

If there is a subsequent medium P (YES in step S116), the process returns to step S102 described above. If there is no subsequent medium P (NO in step S116), wait until the rear end of the medium P passes the discharge sensor 65 (YES in step S117), stop heating the heater 43, and wait for a predetermined period of time. Afterwards, the rotation of the drum motor 27, belt motor 35, and fixing motor 44 is stopped (step S118). This completes the printing operation on the medium P.

Note that when printing on the second or subsequent media P in the same media cassette 11 (NO in step S104), steps S104 to S106 are skipped and the belt motor is activated based on the already set current up flag. 35 drive currents are set (step S107).

This is because the media P in the same media cassette 11 are of the same type and can be considered to have the same slip resistance as the first media P. Further, the second and subsequent media P may be pulled out from the media cassette 11 by the preceding media P, and the accuracy of calculating the time T1 in step S105 may be reduced.

<Effect>
According to the above printing operation, when printing on a non-slippery medium P, the drive current supplied from the motor driver 105 to the belt motor 35 is set higher than when printing on a slippery medium P. The torque of the belt motor 35 (ie, the conveyance force of the conveyor belt 31) is increased. Therefore, even if the load on the belt motor 35 increases due to the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21, the belt motor 35 can continue to rotate without stepping out. As a result, the occurrence of horizontal streaks as shown in FIG. 3 can be suppressed, and printing defects can be reduced.

Furthermore, since it is determined whether or not to increase the driving current of the belt motor 35 based on the time T1 from the start of paper feeding (start of rotation of the paper feeding roller 12) to the detection of the medium by the inlet sensor 62, the medium P It becomes possible to switch the torque of the belt motor 35 according to the slip resistance of the belt motor 35.

In particular, when the paper feed roller 12 sends out the medium P to the conveyance path A1, the medium P is sent out while contacting the separation pad 13, so the time it takes for the medium P to reach the entrance sensor 62 varies depending on the slipperiness of the medium P. Cheap. Therefore, it is possible to switch the torque of the belt motor 35 in accordance with the slipperiness of the medium P accurately.

In addition, the length of the medium P is calculated from the ON/OFF timing of the write sensor 63, and if the length P is shorter than the standard size, the current up flag is turned off. If the time T1 becomes longer for some reason, the torque of the belt motor 35 can be prevented from increasing.

Note that here, as a physical quantity (information) corresponding to the slipperiness of the medium P, the time T1 from when the feeding of the medium P is started until it reaches the entrance sensor 62 is measured. However, the determination is not limited to this example, and the determination may be made based on the time it takes for the medium P to pass between two points on the conveyance path (Embodiment 3, which will be described later). Further, other physical quantities (information) may be used as long as they correspond to the slip resistance of the medium P.

Note that if continuous printing is performed with the driving current of the belt motor 35 increased, the belt motor 35 and the motor driver 105 may become heated. Therefore, when the number of continuously printed sheets exceeds a predetermined number (for example, 100 sheets), it is desirable to perform intermittent printing.

Intermittent printing is a printing method that provides a pause time corresponding to the printing time of 2.5 sheets every time 10 sheets are printed, for example. Thereby, it is possible to suppress heating of the belt motor 35 and the motor driver 105 caused by increasing the driving current of the belt motor 35.

When intermittent printing is performed, the total time required for printing may become longer, but this will be explained in Embodiment 2.

Note that although a stepping motor is used here as the belt motor 35, other types of motors may be used. However, since a stepping motor has the advantage that torque and rotation speed can be easily controlled independently, it is most desirable to use a stepping motor.

<Effects of the embodiment>
As described above, the image forming apparatus 1 according to the first embodiment has a physical quantity corresponding to the slip resistance of the medium P (specifically, from the time when the medium P starts to be fed until it reaches the entrance sensor 62). The driving force of the conveyor belt 31 (that is, the torque of the belt motor 35) is switched according to the time T1). That is, when printing on a non-slippery medium P, the driving force of the conveyor belt 31 is made larger than when printing on a slippery medium P. Therefore, even if the load on the belt motor 35 increases due to the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21, the belt motor 35 can continue to rotate without stepping out, and the horizontal stripe It is possible to suppress the occurrence of printing defects such as.

Embodiment 2.
Next, a second embodiment will be explained. In the first embodiment, when printing on a non-slippery medium P, the torque of the belt motor 35 (driving force of the conveyor belt 31) is set higher than when printing on a slippery medium P. On the other hand, in Embodiment 2, when printing on a non-slippery medium P, the traveling speed of the conveyor belt 31 (that is, the conveyance speed) is lowered than when printing on a slippery medium P, and the photoreceptor The speed difference with the circumferential speed of the drum 21 is reduced.

FIG. 5 is a flowchart showing the printing operation according to the second embodiment. Steps S101 to S105 are as described in the first embodiment. In step S105, if the time T1 from the start of feeding of the medium P until it reaches the inlet sensor 62 is longer than the specified value Th (step S105), the CPU 101 turns on the speed down flag (step S201).

If the speed down flag is ON, the CPU 101 also reduces the number of pulses of the pulse current from the motor driver 105 to the belt motor 35 to lower the rotational speed of the belt motor 35 (step S207).

Specifically, when printing on a non-slippery medium P, the rotational speed of the belt motor 35 is reduced by 0.5%, for example, to reduce the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21. For example, reduce to 0.

When the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21 is reduced, the increase in the load on the belt motor 35 described in the first embodiment is suppressed. Therefore, the occurrence of printing defects such as horizontal stripes can be suppressed without increasing the driving current of the belt motor 35 (that is, without increasing the torque of the belt motor 35).

Note that when reducing the rotational speed of the belt motor 35, it is desirable to reduce the rotational speeds of the paper feed motor 16 and the fixing motor 44 accordingly. It is also desirable to change the numerical value of the specified range of the length L of the medium P in step S113.

The processes after step S202 are the same as described in the first embodiment, except that the process of turning off the speed down flag (step S203) is performed instead of step S114 (turning off the power up flag) of the first embodiment. be.

When increasing the driving current of the belt motor 35 as in the first embodiment described above, the power consumption increases. Furthermore, during continuous printing, intermittent printing may be performed to suppress heating of the belt motor 35 and motor driver 105, which increases the total time required for printing.

On the other hand, in the second embodiment, the drive current of the belt motor 35 is not increased, so power consumption can be reduced. Furthermore, since heating of the belt motor 35 and motor driver 105 is less likely to occur, there is no need to perform intermittent printing, and the total time required for printing can therefore be shortened.

However, in the second embodiment, since the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21 is reduced, there is a possibility that the print quality will be lowered compared to the first embodiment.

Therefore, a mode selection screen, an example of which is shown in FIG. 6, is displayed on the operation panel 113 to allow the user to select either print mode 1, which prioritizes printing speed, or print mode 2, which prioritizes image quality. It's okay.

When print mode 1 is selected, a high quality image can be printed by executing the printing operation shown in FIG. Furthermore, when print mode 2 is selected, by executing the printing operation shown in FIG. 5, the printing time during continuous printing can be shortened.

The image forming apparatus according to the second embodiment has the same configuration as the image forming apparatus 1 according to the first embodiment except for the above-mentioned points.

As described above, in the second embodiment, the physical quantity corresponding to the slipperiness of the medium P (specifically, the time T1 from when the feeding of the medium P is started until it reaches the entrance sensor 62) is Accordingly, the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21 is switched. That is, when printing on a non-slippery medium P, the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21 is made smaller than when printing on a slippery medium P. Therefore, it is possible to suppress an increase in the load on the belt motor 35 and to suppress the occurrence of printing defects such as horizontal stripes.

Embodiment 3.
Next, Embodiment 3 will be described. In the first embodiment described above, the drive current of the belt motor 35 is switched based on the time T1 from the start of feeding of the medium P until the medium P reaches the entrance sensor 62. On the other hand, in the third embodiment, the drive current of the belt motor 35 is switched based on the time it takes for the medium P to move between two points on the conveyance path A1.

FIG. 7 is a diagram showing the basic configuration of an image forming apparatus 1A according to the third embodiment. In the third embodiment, the time from when the leading edge of the medium P passes the paper feed sensor 61 (first sensor) until it reaches the entrance sensor 62 (second sensor) is measured, and the measured time is Based on this, the driving current of the belt motor 35 is switched.

Therefore, a contact member 17 that contacts the medium P is provided in a section from the paper feed sensor 61 to the entrance sensor 62 along the conveyance path A1. Like the separation pad 13, the contact member 17 provides a certain conveyance resistance to the medium P, and is, for example, a pad made of rubber or the like. In this way, it is possible to provide a difference in the time it takes for the non-slippery medium P and the slippery medium P to pass between two points.

The printing operation in the third embodiment is as described in the first embodiment, but in step S105, the time from when the leading edge of the medium P passes the paper feed sensor 61 until it reaches the entrance sensor 62 is calculated. Let it be T1.

If the time T1 is longer than the specified value Th, it is treated as a non-slip medium P, and the driving current of the belt motor 35 is increased. If the time T1 is less than or equal to the specified value Th, it is treated as a slippery medium P, and the drive current of the belt motor 35 is not increased.

Furthermore, in the third embodiment, since the time T1 is not affected by the positional shift of the medium P in the medium cassette 11, the processes of steps S112 to S114 shown in FIG. 4 are not necessary.

The paper feed sensor 61, the entrance sensor 62, and the CPU 101 correspond to a detection unit that detects a physical quantity (here, time T1) corresponding to the slipperiness of the medium P. Here, the time taken for the leading edge of the medium P to reach the entrance sensor 62 after passing the paper feed sensor 61 is measured, but the present invention is not limited to this example. All you have to do is measure the time it takes. It is desirable to arrange a contact member that contacts the medium P between the two points.

The image forming apparatus 1A of the third embodiment is configured in the same manner as the image forming apparatus 1 of the first embodiment except for the above-mentioned points.

As described above, in the third embodiment, the conveying force of the conveying belt 31 (that is, the torque of the belt motor 35) is switched based on the time during which the medium P passes between two points on the conveying path. Therefore, as in the first embodiment, even if the load on the belt motor 35 increases due to the speed difference between the running speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21, the belt motor 35 can rotate without stepping out. The printing process can be continued, and the occurrence of printing defects such as horizontal stripes can be suppressed.

Note that this third embodiment may be applied to the image forming apparatus of the second embodiment. That is, when the time T1 for the medium P to pass between two points on the conveyance path is longer than the specified value T1, the speed difference between the traveling speed of the conveyor belt 31 and the circumferential speed of the photoreceptor drum 21 is reduced. Good too. In this case, as in the second embodiment, it is possible to suppress an increase in the load on the belt motor 35 and to suppress the occurrence of printing defects.

In Embodiments 1 to 3, a configuration has been described in which the toner image from the photoreceptor drum 21 is transferred to the medium P that is transported by the transport belt 31 serving as a transport section, but the transport section is not limited to the transport belt.

In the first to third embodiments, an example in which the image forming apparatus 1 is a printer has been described, but the present disclosure is applicable not only to printers but also to electrophotographic devices such as copying machines, facsimile machines, or MFPs (Multi Function Peripherals). It can be applied to the image forming apparatus used.

Although the preferred embodiments have been specifically described above, the present disclosure is not limited to the embodiments described above, and various improvements and modifications can be made.

Hereinafter, various aspects of the present disclosure will be collectively described as supplementary notes.
(Additional note 1)
an image carrier that carries a developer image;
a conveyance unit that conveys a medium to which a developer image is transferred from the image carrier;
An image forming apparatus comprising: a control unit that detects a physical quantity corresponding to the slipperiness of the medium and switches the conveyance force or conveyance speed of the conveyance unit according to the detected physical quantity.
(Additional note 2)
The image forming apparatus according to appendix 1, wherein the control unit increases the conveyance force of the conveyance unit when conveying a less slippery medium than when conveying a more slippery medium.
(Additional note 3)
The control unit is configured to reduce the speed difference between the conveyance speed of the conveyance unit and the speed of the image carrier when conveying a less slippery medium than when conveying a more slippery medium. The image forming apparatus according to supplementary note 1 or 2.
(Additional note 4)
a paper feeding unit that feeds the medium to the transport unit;
a sensor disposed on the conveyance path of the medium to detect passage of the medium;
According to any one of Supplementary Notes 1 to 3, the physical quantity is the time from when the paper feeding unit starts feeding the medium until the sensor detects the medium. image forming device.
(Appendix 5)
The image forming apparatus according to appendix 4, further comprising a contact member that contacts the medium fed from the paper feeding section.
(Appendix 6)
a paper feeding unit that feeds the medium to the transport unit;
a first sensor and a second sensor that are arranged on the medium conveyance path and detect passage of the medium;
According to any one of Supplementary Notes 1 to 3, wherein the physical quantity is the time from when the first sensor detects the medium to when the second sensor detects the medium. The image forming apparatus described above.
(Appendix 7)
The image forming apparatus according to appendix 6, further comprising a contact member that is disposed between the first sensor and the second sensor in the transport path and contacts the medium.
(Appendix 8)
Supplementary note 4, characterized in that the control unit measures the length of the medium in the conveyance direction, and returns the conveyance force or the conveyance speed switched based on the time according to the measured length. 8. The image forming apparatus according to any one of 7 to 7.
(Appendix 9)
The image forming apparatus according to any one of Supplementary Notes 1 to 8, wherein the surface speed of the image carrier is set to be faster than the transport speed of the transport section by a predetermined percentage.
(Appendix 10)
The conveyance unit is driven by a motor,
The image forming apparatus according to any one of Supplementary Notes 1 to 9, wherein the control unit controls the conveyance force using the torque of the motor.
(Appendix 11)
The image forming apparatus according to appendix 10, wherein the torque of the motor is controlled by a drive current supplied to the motor.
(Appendix 12)
The conveyance unit is driven by a motor,
The image forming apparatus according to any one of Supplementary Notes 1 to 11, wherein the control unit controls the conveyance speed based on the rotational speed of the motor.
(Appendix 13)
The image forming apparatus according to any one of Supplementary Notes 10 to 12, wherein the conveyance section includes a conveyance belt that is driven by a driving force of the motor and conveys the medium.

Reference Signs List 1 image forming apparatus, 10 medium supply unit, 11 medium cassette (medium storage unit), 12 paper feed roller (paper feed unit), 13 separation pad (contact member), 14 transport roller, 16 paper feed motor, 20 image forming unit , 21 Photosensitive drum (image carrier), 22 Charging roller (charging member), 23 Exposure head (exposure device), 24 Developing roller (developer carrier), 25 Supply roller (supplying member), 26 Toner cartridge (developing member). agent container), 27 drum motor, 30 transfer unit, 31 conveyance belt (conveyance section), 32 drive roller (drive section), 33 tension roller, 34 transfer roller (transfer section), 35 belt motor, 40 fixing unit, 41 fixing roller (fixing member), 42 pressure roller (pressure member), 44 fixing motor, 50 medium discharge section, 61 paper feed sensor (first sensor), 62 entrance sensor (sensor, second sensor), 63 writing sensor, 64 65 slack sensor, 66 ejection sensor, 70 housing, 100 control unit, 101 CPU (main control unit), 104 motor driver (paper feed control unit), 105 motor driver (conveyance control unit).

Claims (13)

an image carrier that carries a developer image;
a conveyance unit that conveys a medium to which a developer image is transferred from the image carrier;
An image forming apparatus comprising: a control unit that detects a physical quantity corresponding to the slipperiness of the medium and switches the conveyance force or conveyance speed of the conveyance unit according to the detected physical quantity. The image forming apparatus according to claim 1, wherein the control unit increases the conveyance force of the conveyance unit when conveying a medium that is less slippery than when conveying a medium that is more slippery. . The control unit is configured to reduce the speed difference between the conveyance speed of the conveyance unit and the speed of the image carrier when conveying a less slippery medium than when conveying a more slippery medium. The image forming apparatus according to claim 1. a paper feeding unit that feeds the medium to the transport unit;
a sensor disposed on the conveyance path of the medium to detect passage of the medium;
The image forming apparatus according to claim 1, wherein the physical quantity is a time from when the paper feeding section starts feeding the medium until the sensor detects the medium. The image forming apparatus according to claim 4, further comprising a contact member that contacts the medium fed from the paper feeding section. a paper feeding unit that feeds the medium to the transport unit;
a first sensor and a second sensor that are arranged on the medium conveyance path and detect passage of the medium;
The image forming apparatus according to claim 1, wherein the physical quantity is a time from when the first sensor detects the medium until when the second sensor detects the medium. The image forming apparatus according to claim 6, further comprising a contact member that is disposed between the first sensor and the second sensor in the conveyance path and contacts the medium. The control unit measures the length of the medium in the conveyance direction, and returns the conveyance force or the conveyance speed switched based on the time according to the measured length. 4. The image forming apparatus according to 4. The image forming apparatus according to claim 1, wherein the surface speed of the image carrier is set to be faster than the transport speed of the transport section by a predetermined percentage. The conveyance unit is driven by a motor,
The image forming apparatus according to claim 1, wherein the control unit controls the conveying force using torque of the motor. The image forming apparatus according to claim 10, wherein the torque of the motor is controlled by a drive current supplied to the motor. The conveyance unit is driven by a motor,
The image forming apparatus according to claim 1, wherein the control unit controls the conveyance speed based on the rotational speed of the motor. The image forming apparatus according to claim 10, wherein the conveyance section includes a conveyance belt that is driven by a driving force of the motor to convey the medium.

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