JP2002326738A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device for preventing paper sheet carrying speed from lowering along with roller wearing. SOLUTION: In a paper sheet carrying passage P, a PSS 30 for detecting whether a paper sheet comes from a paper feed cassette is arranged upstream of a photosensitive drum 13 and a transfer roller 21 to judge whether a paper sheet has been sent from a paper feeding cassette, and a PDS 31 is also arranged downstream of a heat roller 23 and a press roller 25 to judge whether a paper sheet which has been sent after the completion of transferring and deposition. The time from when PSS 30 is turned ON to when the PDS 31 is turned ON is measured by a timer TL to detect the time to carry a paper sheet. A printer controller 12 adjusts the pulse rate of a main rotor 41 to keep the carrying speed of a paper sheet constant even if a variety of rollers wear.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus which prevents a reduction in sheet conveyance speed due to abrasion of rollers.

[0002]

2. Description of the Related Art In an image forming apparatus, a sheet is conveyed at a low speed by rotating a motor at a predetermined speed, and an image is formed on the conveyed sheet. In order to convey the paper, various rollers are provided in the paper conveyance path, and the paper is conveyed by rotating each roller by the motor.

For example, in an image forming apparatus of a contact transfer type, a sheet housed in a sheet cassette is transported between a photosensitive drum and a transfer roller by a transport roller, and is transferred between a heating roller and a press roller after transfer. The sheet is conveyed, and after being heated and pressed (after fixing), is conveyed to a discharge tray.

[0004]

However, the surface of the roller gradually wears due to the contact with the paper, and the radius of the roller decreases. In particular, the transport roller that transports the paper in the paper feed cassette to the photosensitive drum and the transfer roller has a greater degree of wear than the other rollers. Nevertheless, the rollers are driven at the same rotational speed as before wear,
The paper transport speed decreases. For this reason, there is a problem in that the image formed on the paper becomes shorter along the paper transport direction due to the wear of the rollers.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an image forming apparatus capable of preventing a reduction in a sheet conveying speed due to abrasion of a roller.

[0006]

According to another aspect of the present invention, there is provided an image forming apparatus for forming an image on a sheet, and conveying the sheet through the image forming section. A paper transport mechanism, a paper transport speed detector that detects the transport speed of the paper, and a controller that controls the paper transport mechanism so that the transport speed of the paper detected by the paper transport speed detector is constant. It is characterized by having.

In this apparatus, the control unit controls the paper transport mechanism so as to keep the paper transport speed constant. Therefore, even if the radius of the roller for transporting the paper gradually decreases due to wear, the paper transport speed is always maintained. Be kept constant. As a result, it is possible to prevent the image formed on the sheet from shrinking in the sheet conveyance direction.

[0008] More specifically, the sheet conveyance speed detecting section is provided after at least two sensors arranged at different positions in the sheet conveyance direction for detecting passage of the sheet and an upstream sensor in the sheet conveyance direction operate. A timer for measuring the time until the downstream sensor operates, and the time measured by the timer is used as information representing the paper transport speed.

The paper transport mechanism includes, for example, a stepping motor as a driving source, and the controller controls the transport speed of the paper to be constant by changing the pulse rate of the stepping motor.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments.

FIG. 1 is a sectional view of a main part of a printer unit of the image forming apparatus according to the embodiment. The outline of the structure of the printer section is as follows. A paper feed roller 40, transport rollers 46 and 47, a photosensitive drum 13 as a photosensitive member, and a transfer member as a transfer member are provided along a paper transport path from a paper feed cassette 45 for setting paper. A transfer roller 21, a heating roller 23 as a fixing device, a press roller 25, and a discharge roller 48 are arranged. Toner is supplied to the photosensitive drum 13 from a toner case 55 by a supply roller 17 and a developing roller 18. Further, the photosensitive drum 13 is charged by the charging brush 14, and an electrostatic latent image corresponding to the image information is formed by the LED print head 16.

An intermediate lid 50 is mounted on the upper surface of the main body so as to be openable and closable. The LED print head 16 is attached to the lower surface of the intermediate cover 50, and when the intermediate cover 50 is closed, the LED print head 16 is positioned at a predetermined relative position with respect to the photosensitive drum 13. Further, an opening / closing cover 51 is attached to the side of the apparatus main body so as to be openable and closable. The opening / closing cover 51 is for releasing a jam or the like of a sheet conveyed in a U-turn. The upper surface of the opening / closing cover 51 serves as a manual paper insertion slot 52.

The paper in the paper feed cassette 45 is
The sheet is taken out one sheet at a time by 0, is conveyed by the conveying rollers 46 and 47, is fed between the photosensitive drum 13 and the transfer roller 21, and the toner image is transferred to the sheet. The sheet on which the toner image has been transferred is heated by the heating roller 23 and the press roller 2.
5, the toner image is fixed, and then discharged by a discharge roller 48 to a discharge tray (not shown).

FIG. 2 (part) and FIG. 3 (remaining part) show schematic block diagrams of the entire image forming apparatus. This image forming apparatus is configured as a so-called multifunction machine having a facsimile function and a copy function.
CU (Network Control Unit) 2, MOD
EM3, ROM4, RAM5, image memory (DRAM)
6. CODEC (Coder and Decoder: Coder and Decoder
7.) Printer I / F (interface) to which operation unit 8, scanner 9, and personal computer 11 are connected
10 is provided.

[0015] The MPU 1 controls each unit constituting the apparatus. The MPU 1 also controls the paper transport mechanism (the paper feed roller 40, the main motor 41, and the like described below) so as to keep the paper transport speed detected by the paper transport speed detection unit (the PSS 30 and the PDS 31 and the timer TL described later) constant. It has a function of controlling various rollers such as the transport rollers 46 and 47). The NCU 2 controls connection with a telephone line network (PSTN), and also has a telephone number (including a FAX number) of a destination.
And a function for detecting an incoming call. MODEM3 is ITU
(International Telecommunication Union)-Recommendation T. 30 based on a facsimile transmission control procedure according to V.30. 17, V.I. 27t
er, V.E. Modulation of the transmission data and demodulation of the reception data according to 29 or the like. Alternatively, in addition to these, The modulation of the transmission data and the demodulation of the reception data according to S.34 are performed.

The ROM 4 stores a program for controlling this device. The RAM 5 temporarily stores data and the like. The image memory 6 temporarily stores received image data and image data read by the scanner 9. COD
EC7 transmits M to read the read image data.
Encoding by H, MR, MMR method, etc.
Then, the received image data is decoded. Operation unit 8
Is for the user to instruct facsimile transmission / reception, printing, and the like. The scanner 9 reads image data of a document when performing fax transmission.

The printer in this apparatus includes a printer controller (control section) 12 for controlling each section of the printer. The printer controller 12 stores a TL register 12a that stores the value of a timer TL that measures the time from when the PSS 30 is turned on to when the PDS 31 is turned on, and a main motor / pulse rate table 12b that stores the pulse rate of the main motor 41, which will be described later. Have. The pulse rate is generated based on the operating frequency of the MPU 1, for example. Further, the printer controller 12 has a current value holding function of holding a current value obtained by a test voltage applied to the transfer roller 21 during standby.

A photosensitive drum 13 having a photoconductive film on the outer peripheral surface as a photosensitive member is arranged inside the printer, and the photosensitive drum 13 is rotated by a driving source (not shown). A charging brush 14 is arranged around the photosensitive drum 13 as a brush roller type charger, and a predetermined bias voltage is applied to the charging brush 14 by a charging bias applying circuit 15. Charging brush 1 to which bias voltage is applied
4 uniformly charges the outer peripheral surface of the photosensitive drum 13 while rotating.

The LED print head 16 as an exposure unit disposed around the photosensitive drum 13 has a number of LEDs arranged in parallel, and irradiates the outer peripheral surface of the photosensitive drum 13 with light based on input image information. Then, an electrostatic latent image corresponding to the image information is formed on the outer peripheral surface.

Further, the developing device disposed around the photosensitive drum 13 is constituted by a supply roller 17, a developing roller 18, a blade 19, a developing device bias applying circuit 20, and the like. The supply roller 17 is provided with a toner case 5 containing toner.
5 (see FIG. 1) while the toner is charged.
A predetermined bias voltage is applied to the supply roller 17 by a developing device bias application circuit 20. A predetermined bias voltage is applied to a developing roller 18 arranged in contact with the supply roller 17 and the photosensitive drum 13 by a developing device bias applying circuit 20.

The blade 19 elastically contacts the outer peripheral surface of the developing roller 18 to make the layer thickness of the toner adhered to the outer peripheral surface of the developing roller 18 uniform. 20 applies a predetermined bias voltage.

Further, a transfer roller 21 as a transfer device disposed around the photosensitive drum 13 is disposed so as to be in contact with the outer peripheral surface of the photosensitive drum 13 with the sheet transport path P interposed therebetween, and a driving source (not shown) Is rotated by This transfer roller 2
1 is applied with a predetermined bias voltage by a transfer bias application circuit 22. The current of the transfer roller 21 is detected by the current detection unit 35, and the detected current value is held in the printer controller 12. Printer controller 1
2 obtains a transfer voltage corresponding to the current value at the time of printing, and the transfer bias application circuit 22 applies the bias voltage to the transfer roller 21.

The fixing device disposed on the sheet feeding side of the sheet transport path P includes a heating roller 23 having a heater such as a halogen lamp, a heater driving circuit 24, a press roller 25, and the like. The heater of the heating roller 23 is heated to a predetermined temperature by a heater driving circuit 24. Heating roller 23
The press roller 25 fixes the toner image on the sheet by heating and pressing the sheet after the transfer by the transfer roller 21.

In this apparatus, a memory removing brush 26 is arranged around the photosensitive drum 13. The memory removing brush 26 is for removing a toner image (memory image) remaining along the outline of the image on the outer peripheral surface of the photosensitive drum 13 even after transfer, and the memory removing brush 26 has a memory removing brush voltage applying circuit. 27 applies a predetermined bias voltage.

Further, in this apparatus, a PSS is provided as a sensor for detecting whether or not a sheet has been fed from a sheet feeding cassette 45 (see FIG. 1) on the sheet conveying path P upstream of the photosensitive drum 13 and the transfer roller 21. (Paper Supply S
PDS as a sensor for detecting whether or not the sheet after the completion of the transfer and fixing has been sent downstream of the heating roller 23 and the press roller 25.
(Paper Discharge Sensor) 31 is provided. As will be described later, the PSS 30 is turned on when a sheet is fed from the paper feed cassette 45, and the PDS 30 is turned on.
31 is ON when the paper after transfer / fixing is sent out
become.

The sheet transport speed detecting section detects the PDS 30 and the PDS 31 and the PDS after the PSS 30 is turned on.
A timer TL for measuring the time until the switch 31 is turned on, and the time measured by the timer TL is used as information representing the paper transport speed.

On the paper supply side, a paper transport mechanism for taking out the paper set in the paper supply cassette 45 one by one is provided. In this paper transport mechanism, a paper feed roller 40 and a main motor (for example, a stepping motor)
41 are connected via a clutch 42 and the paper cassette 4
To take out the paper from the paper feeder 5, the paper feed roller 40 is connected to the main motor 41 by the clutch 42, and the paper feed roller 40 is rotated, whereby the paper in the paper feed cassette 45 is taken out one by one.

In the image forming apparatus constructed as described above, the printing operation is well known. However, in general, the photosensitive drum 13 is uniformly charged by the charging brush 14 and the photosensitive drum 13 is charged by the LED print head 16. An electrostatic latent image corresponding to the image information is formed, and the developing roller 18
As a result, the toner is attracted to the electrostatic latent image on the photosensitive drum 13 and a toner image is formed on the photosensitive drum 13. Then, the toner image on the photosensitive drum 13 is transferred to the sheet by the transfer roller 21. After the transfer, the sheet is heated and pressed by the heating roller 23 and the press roller 25, and the toner image is fixed on the sheet as a permanent image.

In this apparatus, the printer controller 12
However, it is characterized in that the paper transport mechanism is controlled so that the paper transport speed obtained by the PSS 30, PDS 31, and timer TL is constant.

Next, the outline of the printing operation of the image forming apparatus, including the process of keeping the paper conveyance speed constant, will be described with reference to flowcharts of FIGS. 4 to 6 and an operation sequence diagram of FIG. I do.

In the flowchart of FIG. 4, when the printing operation starts, first, in step ST1, the value of the TL register 12a of the printer controller 12 is applied to the table to set the pulse rate of the main motor 41. If no value is stored in the TL register 12a, a default initial value is applied. Next, in step ST2, the main motor 41 is turned on, the charging bias is turned on, the developing bias (+) is turned on, and the transfer bias (-) is turned on.
ON, the memory removal brush 26 is turned ON, and the photosensitive drum 1
The toner of the third uncharged portion is collected by the developing roller 18 and the transfer roller 21 is cleaned.

In the next step ST3, the timer T
1, T6 starts, and in step ST4, it is determined whether or not the timer T1 has timed out, and if not, the process waits. Here, the reason why the developing bias is turned ON at (+) is that the toner remaining on the uncharged portion (the portion where the potential is substantially 0 V) on the outer peripheral surface of the photosensitive drum 13 is efficiently used as a developing device. It is to collect at. The reason why the transfer bias is turned on at (−) is to collect the toner adhered to the outer peripheral surface of the transfer roller 21 to the outer peripheral surface of the photosensitive drum 13.

When the timer T1 times out, in step ST5, the developing bias (-) is switched and the transfer bias is turned off. Then, in step ST6, the timer T2 is started, and in step ST7, it is determined whether or not the time of the timer T2 is up. When the timer T2 expires, in step ST8, a test voltage is applied to the transfer roller 21, and an FB sequence (feedback sequence) is started.

In the next step ST9, the timer T
3 starts, and in step ST10, the current value of the transfer roller 21 is detected by the current detection unit 35, and the current value is sampled. In step ST11, it is determined whether or not the time of the timer T3 has expired. If not, the process returns to step ST10 to sample the current value, that is, FB
Continue the sequence.

When the timer T3 times out, in step ST12, the sampled current value is held in the printer controller 12, and then the process proceeds to step ST13.
, The transfer bias is turned off. Then, in step ST14, the timer T4 is started, and in step ST15, it is determined whether or not the time of the timer T4 is up. When the time is up, in step ST16, the transfer bias (-) is turned on, and the transfer roller 2 is turned on again.
Clean 1

Subsequently, in step ST17, the timer T5 is started. In step ST18, it is determined whether or not the timer T5 has timed out. When the time is up, the transfer bias is turned off in step ST19.
To Further, in step ST20, the timer T6
It is determined whether or not the time has elapsed, and when the time has elapsed, it is determined in step ST21 whether the temperature rise of the fixing device (the heating roller 23 and the press roller 25) has been completed.

When the temperature rise of the fixing unit is completed, step ST
At 22, the paper feed clutch 42 is turned on, and at step ST23, the timer T7 starts. In step ST24, it is determined whether or not the PSS 30 has been turned on. If the PSS 30 has been turned off, it is determined in step ST25 whether or not the timer T7 has expired. PSS3 before timer T7 expires
If 0 remains OFF, it means that the paper has not been sent from the paper supply cassette 45 to the PSS 30 due to a paper jam or the like, and the process proceeds to step ST26.
In step ST26, the main motor 41, the charging bias, the developing bias, the transfer bias, the memory removing brush 26, and the fixing device are all turned off.
, A jam is displayed, and the print processing ends.

On the other hand, in step ST24, the PSS
When 30 is turned on, the process proceeds to step ST28. In step ST28, the timers T8, T9,
T10 and TL start. In step ST29, it is determined whether or not the time of the timer T8 has expired. When the time has expired, in step ST30, exposure of the electrostatic latent image is started. In the next step ST31, it is determined whether or not the time of the timer T9 has expired. When the time has expired, a pre-transfer bias is applied to the transfer roller 21 in step ST32.

Next, in step ST33, it is determined whether or not the timer T10 has timed out. When the time has expired, in step ST34, the transfer bias determined by the FB sequence, that is, the transfer bias corresponding to the current value obtained by the sampling, is applied. The determined transfer bias (+) is transferred to the transfer roller 21.

Then, in step ST35, it is determined whether or not the timer TL has expired. If not, it is determined in step ST36 whether the PDS 31 has been turned on. If the PDS 31 is turned on, it means that the transferred and fixed paper has been sent, and therefore, step ST3
In step 7, the count value of the timer TL is set in the TL register 12a of the printer controller 12. Thereafter, the printing process is continued.

When the PDS 31 is OFF in step ST36, since the transferred / fixed sheet has not been sent yet, the process returns to step ST35, and the timer TL is reset again.
It is determined whether the time is up. Here, if the PDS 31 is turned on before the timer TL times out,
This means that the paper has been conveyed within a certain period of time from when the PSS 30 is turned on to when the PDS 31 is turned on. That is, the printing operation is normal.

However, if the PDS 31 remains OFF before the timer TL expires, the PS
Since it is considered that a paper jam or the like has occurred in the process after the ON of S30, the determination in step ST35 is YES, and the process proceeds to step ST26.
As described above, after the main motor 41, the charging bias, the developing bias, the transfer bias, the memory removing brush 26, and the fixing device are all turned off, the process proceeds to step ST2.
At 7, a jam is displayed, and the printing process ends.

Next, the drive sequence of the main motor 41 is as shown in FIG. 8 in the case of two-phase excitation, for example. To keep the paper transport speed constant, when the rollers (the transport rollers 46 and 47, the transfer roller 21, the heating roller 23, the press roller 25, and the like, especially the transport rollers 46 and 47) are not worn, If the diameter is large, increase the pulse rate and the rollers will wear due to contact with the paper,
As the outside diameter decreases, the pulse rate is gradually reduced. As a result, it is possible to increase the paper transport speed in accordance with the wear of the roller, and to prevent a reduction in the print length due to a decrease in the roller diameter.

In the above embodiment, the main motor 4
Although the pulse rate of 1 is stored in the pulse rate table 12b of the printer controller 12, the pulse rate may be obtained by simple arithmetic processing.

The main motor 41 is not limited to a stepping motor, but may be a synchronous motor or the like. FIG. 8 shows a two-phase excitation system.
Other excitation methods such as two-phase excitation are also applicable.

Further, the paper transport speed is detected simply and accurately by using two sensors (PSS 30 and PDS 31) and a timer TL, but the present invention is not limited to this. A speed sensor is also applicable.

[0047]

As described above, according to the image forming apparatus of the first aspect of the present invention, regardless of the abrasion of the rollers, the paper conveyance speed is always kept constant, so that the image is formed on the paper. It is possible to prevent the image to be shrunk along the sheet conveyance direction.

According to the second aspect of the present invention, since the paper transport speed is measured by the two sensors and the timer, the paper transport speed can be accurately detected with a simple configuration.

Further, according to the configuration of the third aspect, since the pulse rate of the stepping motor is adjusted, fine adjustment can be performed, and the paper transport speed can always be maintained accurately and constantly.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a printer unit of an image forming apparatus according to an embodiment.

FIG. 2 is a schematic block diagram (a part) of the entire image forming apparatus.

FIG. 3 is a schematic block diagram (remaining portion) of the entire image forming apparatus.

FIG. 4 is a flowchart showing a printing operation of the image forming apparatus.

FIG. 5 is a flowchart that follows the flowchart of FIG. 4;

FIG. 6 is a flowchart that follows the flowchart of FIG. 5;

FIG. 7 is an operation sequence diagram of the image forming apparatus.

FIG. 8 is a drive sequence diagram of a two-phase excitation type stepping motor as a motor used in a sheet transport mechanism of the image forming apparatus.

[Description of Signs] 1 MPU 12 Printer Controller 12a TL Register 12b Main Motor / Pulse Rate Table 13 Photosensitive Drum 14 Charging Brush 16 LED Print Head 18 Developing Roller 21 Transfer Roller 23 Heating Roller 25 Press Roller 30 PSS 31 PDS 40 Feed Roller 41 Main motor 42 Paper feed clutch

Continued on the front page F-term (reference) 2H027 DA20 DA39 DC03 DC11 DE07 ED16 EE03 EE04 EE07 EE08 EF09 EF10 2H072 AA02 AA16 AA17 AA29 AB09 BA03 CA01 JA02 3F048 AA01 AB01 BA05 BA14 BB02 CC03 CC12 DA06 DB07 DB11 DC00 LB03

Claims (3)

[Claims] An image forming section for forming an image on a sheet, a sheet conveying mechanism for conveying a sheet through the image forming section, a sheet conveying speed detecting section for detecting a sheet conveying speed, and a sheet conveying speed detecting section An image forming apparatus comprising: a control unit configured to control a sheet conveying mechanism so that a sheet conveying speed detected by the control unit is constant. 2. The apparatus according to claim 1, wherein the sheet transport speed detecting section is provided at least two sensors disposed at different positions in the sheet transport direction to detect the passage of the sheet and a downstream sensor after an upstream sensor in the sheet transport direction operates. 2. The image forming apparatus according to claim 1, further comprising a timer for measuring a time until the sensor on the side operates, wherein the time measured by the timer is used as information indicating a sheet conveying speed. 3. The paper transport mechanism section includes a stepping motor as a drive source, and the control section controls the paper transport speed to be constant by changing a pulse rate of the stepping motor. Or the image forming apparatus according to claim 2.