JP3832906B2 - Image recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention forms and supports an unfixed image corresponding to target image information on a recording paper (recording medium) by an appropriate image forming process mechanism such as an electrophotographic system, an electrostatic recording system, a magnetic recording system, etc. The present invention relates to an image recording apparatus (image forming apparatus) such as a laser printer, a copying machine, etc., which introduces the toner image into a fixing device (image heat fixing apparatus) and heat-fixes an unfixed image on a recording sheet to output an image recorded matter.
[0002]
[Prior art]
For convenience, a laser printer using a transfer type electrophotographic process will be described as an example. In the printer, an electrophotographic photosensitive member (image carrier, hereinafter referred to as a photosensitive drum) generally having a rotating drum type is driven to rotate at a predetermined peripheral speed (process speed), and the surface of the rotating photosensitive drum is charged. Rotate by charging with a laser beam modulated to correspond to the time-series electrical digital pixel signal of the target image information, which is charged to a predetermined polarity and potential, and the charged surface is output from the laser scanner unit. An electrostatic latent image corresponding to target image information is formed on the photosensitive drum surface. The electrostatic latent image is developed as a toner image by the developing unit, and the toner image is transferred by the transfer unit to the recording paper fed from the paper feeding unit side to the transfer unit of the rotary photosensitive drum at a predetermined timing. . Then, the recording paper to which the toner image (unfixed image) is transferred is introduced into the fixing means, and the toner image is fixed on the recording paper as a permanently fixed image and output as an image formed product (print, copy). .
[0003]
1) As a fixing means for fixing an unfixed image formed and supported on a recording paper, a heat roller type fixing device is generally used. The heat roller type fixing device incorporates a halogen heater as a heat source, and a fixing roller (heat roller) heated to a predetermined temperature by the heat generated by the halogen heater, and a silicon roller. - A fixing nip is formed by pressing a pressure roller formed of a heat-resistant material having a predetermined elasticity, such as rubber, and the roller pair is rotated. A recording paper on which an unfixed toner image is formed and supported is introduced and nipped and conveyed, whereby heat is applied from a fixing roller and pressure is applied to fix the toner image on the recording paper. However, the heat roller type fixing device has a large heat capacity of the fixing roller, and energizes the halogen heater as a heat generation source until the fixing roller rises from a normal temperature state to a predetermined fixing temperature to be in a temperature controlled state. It takes considerable warming time and lacks quick start. In addition, the halogen heater is energized to keep the fixing roller in an overheated state even when the printer is not in use so that the image forming operation can be executed immediately whenever the fixing roller is raised from the normal temperature state to a predetermined fixing temperature. The halogen heater as a heat generation source has a problem that power consumption is large because electric energy is temporarily converted into light because of low energy efficiency. Further, even when the printer is not used, energizing the halogen heater to maintain the fixing roller in a preheated state causes the temperature inside the apparatus to be unnecessarily increased by heat radiation from the fixing roller.
[0004]
2) Therefore, in recent years, on-demand type fixing devices are becoming mainstream instead of heat roller type fixing devices from the viewpoint of quick start and power saving.
[0005]
As an on-demand type fixing device, for example, a film heating type device is known. In this apparatus, a heating member having a low heat capacity such as a ceramic heater and a thin heat transfer film material such as polyimide are used to reduce the heat capacity of the heating member.
[0006]
More specifically, as disclosed in JP-A-63-313182, a heat resistant film is generally sandwiched between a ceramic heater as a heating element (a heat generation source) and a pressure roller as a pressure member. Then, a fixing nip is formed, and a recording paper on which an unfixed toner image is formed and supported is introduced between the heat resistant film and the pressure roller of the fixing nip, and the fixing nip is formed together with the heat resistant film. By sandwiching and conveying, the heat of the ceramic heater is applied to the recording paper through a heat resistant film and heated to heat and fix the toner image on the recording paper.
[0007]
Such a film heating type fixing device uses a ceramic heater or a film having a low heat capacity as a heating element and has a good temperature response, so that the fixing nip portion is quickly raised to a required fixing temperature by energizing the heater. Therefore, the temperature can be controlled and quick start can be achieved, and the heater can be turned off when paper is not being fed, thereby saving power. In-machine temperature rise can also be suppressed.
[0008]
The heating element is an electromagnetic induction exothermic member, or the film is an electromagnetic induction exothermic member, and they generate electromagnetic induction heat (heat generation due to eddy current loss) by the action of the alternating magnetic field generated by the alternating magnetic field generating means. Also known are electromagnetic induction heating type fixing devices that heat the recording paper and heat-fix the toner image on the recording paper, and these are also on-demand types and have quick start and power saving.
[0009]
In an on-demand type fixing device as in the above example, a heat source film or electromagnetic induction heat generating film as a moving body on the heating member side is provided by providing a drive source on the pressure roller side and rotating the pressure roller. The recording paper introduced into the fixing nip portion is conveyed by the rotational driving force of the pressure roller, and is nipped and conveyed together with the film (pressure roller driving system, Japanese Patent Laid-Open No. Hei 4). -44075 to 44083, 2042080 to 204984, etc.).
[0010]
[Problems to be solved by the invention]
As described above, the on-demand type fixing device is effective with quick start and power saving, but there are the following problems in the case of the pressure roller driving method.
[0011]
That is, in the case of a pressure roller driving type fixing device, the recording paper conveyance speed in the fixing nip portion is governed by the diameter of the pressure roller, so the pressure roller when the pressure roller is cold at the beginning of recording. Compared to the recording paper conveyance speed at the fixing nip portion due to the diameter (initial diameter), during continuous recording, the pressure roller is gradually heated by the heat of the heating member and thermally expanded, and the diameter becomes larger than the initial diameter. In this state, a fluctuation phenomenon occurs in which the recording paper conveyance speed at the fixing nip portion is increased due to the pressure roller diameter.
[0012]
For this reason, when the recording operation is continued, the recording paper conveyance speed in the fixing nip portion of the fixing device becomes higher than the recording paper conveyance speed (predetermined process speed) in the transfer unit (image forming unit), resulting in a difference between the two. When the recording paper is transported through the transfer section at a predetermined process speed and undergoes toner image transfer, the recording paper passes through the transfer section and reaches the fixing nip portion of the fixing device. The paper is conveyed at a recording paper conveyance speed in the fixing nip portion of the fixing device, which is higher than the recording paper conveyance speed which is a predetermined process speed in the transfer unit.
[0013]
Therefore, the toner image (recording image) transferred to the recording paper area after the pressure roller of the fixing device and the area between the transfer portions of the recording paper when the leading edge of the recording paper reaches the fixing nip portion of the fixing device. ) Is stretched in the recording paper transport direction because the recording paper is pulled and transported at a recording paper transport speed at the fixing unit fixing nip larger than the recording paper transport speed, which is a predetermined process speed in the transfer section. That is, the image is extended (elongated). Depending on the case, the rear end of the image may be detached from the rear end of the recording paper due to the image extension.
[0014]
FIG. These are graphs showing an example of the relationship between the number of recorded sheets and the recorded image extension rate. In this image recording apparatus, when 30 sheets are continuously recorded, the recorded image is extended by about 1% from the initial stage. After that, even if continuous recording is continued, the diameter increasing gradient due to the thermal expansion of the pressure roller is almost 0. Thus, the image extension rate is saturated. Therefore, the 30th recorded image is about 3 mm longer than the 1st recorded image if it is A4 size.
[0015]
FIG. The left half of the figure is the first output recording paper. In this case, since the pressure roller of the fixing device is cooled and in the initial diameter state at the beginning of recording, the fixing nip portion of the fixing device is The recording paper conveyance speed is almost the same as the recording paper conveyance speed in the transfer unit, and the recording paper is almost the same as the recording paper conveyance speed in the transfer unit even after the leading edge reaches the fixing nip part of the fixing device from the transfer unit. Thus, there is no pulling conveyance of the recording paper in the transfer nip portion, so that the recording image formed on the recording paper does not substantially extend in the entire area portion from the front end to the rear end.
[0016]
FIG. The right half of the figure is the 30th output recording paper. In this case, as described above, the pressure roller is gradually heated and thermally expanded by the heat on the heating member side during the continuous recording so far, and the diameter is increased. Is larger than the initial diameter, and therefore the recording paper conveyance speed at the fixing nip of the fixing device is faster than the recording paper conveyance speed at the transfer unit. When the recording paper reaches the fixing nip portion of the printer, the recording image portion corresponding to the region between the pressure roller and the transfer portion of the fixing device has no image extension, but corresponds to the subsequent recording paper region portion. The recorded image portion is an image extended in the recording paper conveyance direction for pulling conveyance. For this reason, if an image of 2 mm is continuously recorded on the A4 size recording paper to the rear end, the image of about 3 mm is extended and an image defect of 1 mm is generated at the 30th sheet.
[0017]
Accordingly, the present invention solves the above-described problems with respect to an image recording apparatus provided with a pressure roller driving system / on-demand type fixing device as an image fixing means, that is, prevents the extension of a recorded image during continuous recording, The purpose is to reduce the change in image magnification within one page of recording paper.
[0018]
[Means for Solving the Problems]
The present invention is an image recording apparatus characterized by the following configuration.
[0019]
Rotate An image carrier; Has polygon mirror and polygon mirror drive motor The image carrier according to image information Laser scanner And a recording paper having a pressure roller for conveying the recording paper and carrying an unfixed image transferred from the image carrier. At the fixing nip Fixing means for nipping and conveying and fixing an unfixed image on recording paper by heating, the image carrier and the pressure roller All recording paper transport members in the recording paper transport path including Drive Maine A motor, The distance between the image transfer position from the image carrier to the recording paper and the fixing nip is shorter than the conveyance direction size of at least one size of recording paper that can be used in the apparatus. In the image recording device,
Said At the fixing nip In the state of being nipped and transported One piece Measuring means for measuring the time for the recording paper to pass a predetermined position in the recording paper transport path; and Maine Motor and said For polygon mirror drive Control means for controlling the motor, the control means It takes for a sheet of recording paper to pass through the predetermined position. Measurement time Reference time required for the recording paper to pass the predetermined position Than Short The above For polygon mirror drive Without changing the motor drive speed Maine Reduce motor drive speed Then, by reducing the drive speed of the main motor, the magnification of the image formed on the image carrier in the rotation direction of the image carrier is reduced from a reference magnification, and the recording paper is conveyed onto the recording paper at the image transfer position. The magnification in the direction is prevented from being larger than the reference magnification due to the pulling of the recording paper due to the increase in the recording paper conveyance speed in the fixing nip portion. An image recording apparatus.
[0020]
[0021]
[0022]
[0023]
[0024]
[0025]
<Action>
That is, the present invention Is Fixing by measuring the time for the recording paper to pass a predetermined position and changing the recording paper conveyance speed based on the measurement result means of Pressure roller This cancels the change in the recording paper conveyance speed caused by the thermal expansion of the recording paper and prevents the recording image from extending.
[0026]
[0027]
[0028]
DETAILED DESCRIPTION OF THE INVENTION
<Embodiment Example 1> (FIGS. 1 to 9)
(1) Image recording device example
FIG. 1 is a schematic configuration diagram of an example of an image recording apparatus. The image recording apparatus 1 of this example is a laser printer using a transfer type electrophotographic process.
[0029]
Reference numeral 18 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed).
[0030]
The photosensitive drum 18 is uniformly charged to a predetermined polarity and potential by the primary charging roller 19 during the rotation process. By the laser beam modulated and controlled (ON / OFF control) corresponding to the time series electric digital pixel signal of the target image information output from the laser scanner unit 8 to the uniformly charged surface of the rotating photosensitive drum 18. By performing scanning exposure L, an electrostatic latent image of target image information is formed on the surface of the rotary photosensitive drum 18.
[0031]
The formed latent image is developed with toner by the developing device 20 and visualized. As a development method, a jumping development method, a two-component development method, a FEED development method, or the like is used, and is often used in combination with image exposure and reversal development.
[0032]
On the other hand, a recording sheet (transfer material) S as a recording medium accommodated in the sheet feeding cassette 2 is fed to one sheet by driving the sheet feeding roller 5, and a photosensitive drum 18 is coupled with a sheet feeding / conveying roller pair (registration roller) 6. The sheet is fed at a predetermined control timing to a transfer nip T which is a pressure contact portion with the transfer charging roller 21. Reference numeral 7 denotes a paper feed sensor provided on the downstream side in the recording paper transport direction with respect to the paper feed transport roller pair 6 and detects the transport state of the fed recording paper.
[0033]
By feeding the recording sheet S to the transfer nip T, the toner image on the surface of the photosensitive drum 18 is sequentially transferred onto the surface of the feeding recording sheet S. The recording paper S exiting the transfer nip T is sequentially separated from the surface of the rotary photosensitive drum 18 and is introduced into a fixing device 10 as a heating device for heat-fixing the toner image to perform heat-fixing processing of the toner image. receive. The fixing device 10 of this example will be described in detail in the next section (2).
[0034]
The recording paper exiting the fixing device 10 is printed out on the stacking tray 13 by the paper discharge roller 12.
[0035]
Further, the surface of the rotating photosensitive drum 18 after separation of the recording paper is subjected to a removal process of adhering contaminants such as transfer residual toner by a cleaner 22 and is repeatedly subjected to image formation.
[0036]
In the printer 1 of this example, four process devices including a photosensitive drum 18, a primary charging roller 19, a developing device 20, and a cleaner 22 are collectively provided as a process cartridge (image forming unit) 9 detachably attached to the printer body.
[0037]
In the laser scanner unit 8, reference numeral 14 denotes a laser unit that emits laser light modulated based on an image signal (image signal VDO) sent from an external device 30 such as a personal computer. A polygon mirror 15 scans the photosensitive drum 18 with laser light from the laser unit 14, and 15a a motor for rotating the mirror (polygon mode). T) , 16 is an imaging lens group, and 17 is a folding mirror. 3 is a cassette paper presence / absence sensor that detects the presence or absence of the recording paper S in the cassette 2, 4 is a cassette size sensor (consisting of a plurality of microswitches) that detects the size of the recording paper S in the cassette 2, and 11 is a discharge It is a paper discharge sensor that detects the recording paper conveyance state of the paper section.
[0038]
23 is the main mode In A driving force is applied to the paper feed roller 5 through the paper feed roller clutch 24, and each unit in the image forming unit 9 including the paper feed / conveying roller pair 6 and the photosensitive drum 18, the fixing device 10, and paper discharge A driving force is also applied to the roller 12 and the like.
A printer control device (engine controller) 26 controls the printer main body 1 and includes an MPU (microcomputer) having a timer, a ROM, a RAM, and the like, various input / output control circuits, and the like.
[0039]
The printer control device 26 is connected to a video control device (video controller) 28 via a video interface 27 which is an internal communication means, and the video control device 28 is connected to a personal computer or the like via a general-purpose interface 29 such as a Centronics interface. The external device 30 is connected.
[0040]
The video control device 28 converts image information transmitted from the external device 30 to the printer main body 1 via the general-purpose interface 29 into a video signal, and transmits the video signal to the printer control device 26 via the video interface 27.
[0041]
(2) Fixing device 10
FIG. 2 is an enlarged cross-sectional model view of the main part of the fixing device 10. The fixing device 10 of this example is a so-called on-demand type, tensionless type, pressure roller driving type film heating type device disclosed in Japanese Patent Application Laid-Open Nos. 4-44075 to 44083, Japanese Patent Application No. 4-20420 to 204984, and the like. is there.
[0042]
That is, a cylindrical (endless) heat-resistant film (fixing film) 10c is used as a heating moving body, and at least a part of the circumference of the film is tension-free (a state in which no tension is applied), and the film 10c is added. It is configured to be rotationally driven by a rotational driving force of a pressure roller 10e as a pressure member (pressure rotator).
[0043]
Reference numeral 10d denotes a film inner surface guide stay (stay) having a substantially semicircular arc-shaped saddle shape having rigidity and heat insulation. I'm allowed. The cylindrical film 10c is loosely fitted on the stay 10d including the heater 10a.
[0044]
The pressure roller 10e includes a cored bar 10f and a heat-resistant elastic layer 10g such as a silicone rubber layer excellent in releasability formed concentrically and integrally on the outer periphery of the cored bar. The film 10c is sandwiched between the heaters 10a with a predetermined pressing force by means, and is arranged in mutual pressure contact with the heater 10a. N is the pressure nip (heating nip / fixing nip). The pressure roller 10e has a main mode. 2 3, the rotational driving force is transmitted through a power transmission system (not shown), and is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed.
[0045]
A rotational force acts directly on the film 10c by the frictional force between the roller 10e and the outer surface of the film by the rotation of the pressure roller 10e (when the recording paper S is introduced into the nip portion N, the recording paper S is The film 10c indirectly rotates), and the film 10c rotates by following the clockwise direction indicated by the arrow while sliding against the lower surface of the ceramic heater 10a.
[0046]
The film inner surface guide stay 10d facilitates the rotation of the film 10c. In order to reduce the sliding resistance between the inner surface of the film 10c and the surface of the ceramic heater 10a, a small amount of lubricant such as heat-resistant grease may be interposed between them.
[0047]
The ceramic heater 10a is heated by power supply to the energizing heating element b of the ceramic heater 10a, and the rotating film 10c is heated in the nip portion N by the generated heat. Then, the recording paper S is introduced between the film 10c and the pressure roller 10e in the nip portion N with the unfixed toner image carrying surface facing the film 10c, so that the recording paper S adheres to the film 10c. Then, the nip portion N is nipped and passed through at a speed corresponding to the rotational peripheral speed of the pressure roller 10e in an overlapping state with the film.
[0048]
Thermal energy is applied to the recording paper S from the film 10c heated by the ceramic heater 10a in the process of passing the nip portion of the recording paper S, and the unfixed toner image t on the recording paper S is heated and melted and fixed. After passing through the nip portion N, the recording paper S is separated from the surface of the film 10c and discharged.
[0049]
The film 10c has a total thickness of 100 μm or less, preferably 20 μm or more and 40 μm or less in order to reduce the heat capacity and improve the quick start property. The material is PTFE, PFA, FEP monolayer with heat resistance, releasability, strength, durability, etc., or PTFE, PFA on the film surface such as polyimide, polyamideimide, PEEK, PES, PFA, FEP. , A composite layer film coated with FEP or the like as a release layer.
[0050]
The ceramic heater 10a serving as a heating element has a long length in the direction perpendicular to the conveyance direction of the film 10c or the recording paper S in the heating nip portion N, for example, a long and thin heat resistance, insulation, and good heat. A heater substrate a made of conductive alumina or the like, and an electric resistance material such as Ag / Pd (silver palladium), for example, at a thickness of about 10 μm and a width of 1 to The heating heating element b formed by coating by screen printing or the like on 3 mm, the feeding electrodes at both longitudinal ends of the heating heating element, glass or fluororesin coated on the heater surface on which the heating heating element b is formed This is a linear heating body with a low heat capacity as a whole, comprising a protective layer c, a thermistor d as a heater temperature detection means provided on the back side of the heater substrate.
[0051]
This ceramic heater 10a is exposed downward on the surface side on which the energization heating element b is formed, so that the film inner surface guide step is exposed. I The outer bottom surface of 10d is fixedly supported.
[0052]
The ceramic heater 10a rises in temperature when the energization heating element b generates heat over the entire length by feeding power to the power supply electrodes at both ends of the energization heating element b. The temperature of the heater is detected by a thermistor d which is a temperature detecting means, and the output of the thermistor d is A / D converted and taken into the printer control device 26. Temperature control is performed so that the temperature of the ceramic heater 10a, that is, the temperature of the fixing device is maintained at a predetermined temperature by setting the AC voltage supplied to the energization heating element b to a desired value by phase, wave number control, or the like. . That is, by controlling energization to the energization heating element b so that the ceramic heater 10a is heated when the heater detection temperature of the thermistor d is lower than a predetermined set temperature, and when it is higher, the ceramic heater 10a is cooled. The temperature of the ceramic heater 10a is adjusted so as to keep a predetermined constant value during fixing.
[0053]
The fixing device 10 as a heating device of the film heating system as in this example can use a ceramic heater 10a or a fixing film 10c as a heat generation source having a low heat capacity, can be quickly raised in temperature, has a quick start property, and It is a power-saving on-demand device that does not require preheating energization.
[0054]
In addition, the tensionless type film heating type fixing device 10 as in this example includes a nip portion N, a film inner surface guide stay outer surface portion upstream of the nip portion N and the nip portion N in the film rotation direction, and the film. Tension acts only on the film portion in the contact area, and tension does not act on the remaining most film portion. Therefore, the shifting force along the stay length of the film 10c in the film rotation driving state is small, and the film shifting control means or the film shifting control means can be simplified. For example, the film shift movement restricting means can be as simple as a flange member for receiving the film end, and the film shift control means can be omitted to reduce the cost and size of the apparatus.
[0055]
(3) Video interface 27
FIG. 3 is a schematic diagram illustrating the configuration of the video interface 27.
[0056]
CPRDY: a signal indicating that the external device 30 can communicate, and is sent from the video control device 28 to the printer control device 26.
[0057]
PPRDY: A signal indicating that the printer control device 26 can communicate, and is sent from the printer control device 26 to the video control device 28.
[0058]
SBSY: a status valid signal, which is sent from the printer controller 26 to the video controller 28.
[0059]
CBSY: A command valid signal, which is sent from the video controller 28 to the printer controller 26.
[0060]
SC: Status / command signal, and when the status valid signal SBSY is TRUE, it is sent from the printer control device 26 to the video control device 28 as status data indicating the internal state of the printer, and when the command valid signal CBSY is TURE. The video control device 28 sends command data indicating a command to the printer from the video control device 28 to the printer control device 26.
[0061]
CLK: a synchronous clock of the status / command signal SC, which is sent from the video controller 28 to the printer controller 26. In response to one command from the external device 30, the printer control device 26 returns one status corresponding to the command.
[0062]
That is, handshake serial communication is performed using the SBSY, CBSY, SC, and CLK signals.
[0063]
RDY: When the printer control device 26 is ready to print with a ready signal, it is set to TRUE and is sent from the printer control device 26 to the video control device 28.
[0064]
PRINT; a print signal that becomes TRUE when the external device 30 instructs to start printing, and is sent from the video control device 28 to the printer control device 26.
[0065]
TOP: A vertical synchronizing signal for synchronizing the vertical direction (sub-scanning direction / paper conveying direction) of the image output sent from the printer control device 26 to the video control device 28.
[0066]
HSYNC: a horizontal synchronizing signal for synchronizing the horizontal direction (main scanning direction / laser scanning direction) of the image output sent from the printer control device 26 to the video control device 28.
[0067]
VDO: An image signal in which the video control device 28 serially sends dot images to the printer control device 26 in synchronization with the vertical synchronization signal TOP and the horizontal synchronization signal HSYNC.
[0068]
(4) Serial communication operation
FIG. 4 is a timing chart showing the operation of the serial communication.
[0069]
When the printer main body 1 is turned on, the initialization of the printer control device 26 is completed, and the serial communication is enabled, the printer control device 26 sets PPRDY to TRUE.
[0070]
On the other hand, when the video control device 28 is turned on, initialization and the like are completed, and the serial communication is ready, the video control device 28 sets CPRDY to TRUE. The video control device 28 determines that serial communication is possible when it confirms that PPRDY is TRUE for a predetermined time, and if necessary, sets CBSY to TRUE, synchronizes with CLK, and sets an 8-bit value from the SC line. Send a command. Thereafter, CBSY is set to FALSE, and a status return from the printer control device 26 is awaited.
[0071]
When the printer control device 26 receives the command, the printer control device 26 sets SBSY to TRUE to return a status corresponding to the content. When the video control device 28 detects SBSY TRUE, the video control device 28 starts transmission of CLK, the printer control device 26 returns the status from the SC line in synchronization with CLK, and sets SBSY to FALSE. When the printer control device 26 confirms CPRDY TRUE for a predetermined time, the printer control device 26 determines that serial communication is possible and determines that the command is valid.
[0072]
(5) Normal printing operation of the printer 1
5A and 5B are timing charts showing a normal printing operation of the printer 1. FIG.
[0073]
In FIG. 5A, when the printer control device 26 is ready to accept printing, RDY is set to TRUE, and the video control device 28 is notified that printing is acceptable.
[0074]
In response to this, when a print request from the external device 30 is generated, the video controller 28 sets PRINT to TRUE and instructs the start of printing.
[0075]
When the printer control device 26 detects PRINT TRUE, it starts driving the main motor 23 and the polygon motor 15 a of the laser scanner unit 8.
[0076]
When the main motor 23 is driven, the driving force is transmitted to the paper feeding / conveying roller 6, the photosensitive drum 18, the fixing device 10, the primary charging roller 19, the developing device 20, the transfer roller 21, and the paper discharge roller 12. At this time, predetermined high voltage application driving is also performed on the primary charging roller 19, the developing device 20, the transfer charging roller 21, and the like.
[0077]
Further, heating of the ceramic heater 10a in the fixing device 10 is started, and the heater (fixing) is controlled by controlling the energization duty to the energization heating element b of the ceramic heater 10a so that the heater temperature detected by the thermistor d becomes 170 ° C. Temperature).
[0078]
The printer control device 26 turns on the sheet feeding clutch 24 for t2 seconds after the rotation of the polygon motor 15a reaches a steady state to drive the sheet feeding roller 5 and feeds the recording sheet S toward the sheet feeding and conveying roller 6. Make paper.
[0079]
When the printer control device 26 detects that the leading edge of the recording paper S has passed through the paper feed roller 6 and reached the paper feed sensor 7, the printer control device 26 sends a vertical synchronization signal TOP to the video control device 28 after a predetermined time t3 seconds. Send it out.
[0080]
The video controller 28 starts outputting the image signal VDO for one page after tv seconds in synchronization with TOP.
[0081]
During this time, the printer control device 26 sends a horizontal synchronization signal HSYNC to the video control device 28 at a predetermined timing synchronized with the laser scanning, and modulates the laser light emitted from the laser unit 14 based on the image signal VDO.
[0082]
As shown in FIG. 5B, the video control device 28 outputs the image signal VDO for one scan after th seconds in synchronization with the rising of the horizontal synchronization signal HSYNC.
[0083]
Through the operation as described above, the recording sheet S is sequentially conveyed to the sheet feeding roller 5, the sheet feeding / conveying roller 6, the transfer nip T of the image forming unit 9, the fixing device 10, and the sheet discharging roller 12 to record an image. The
[0084]
When the trailing edge of the recording paper S is detected by the paper discharge sensor 11, the temperature control of the ceramic heater 10a of the fixing device 10 is stopped, and high voltage application driving to the primary charging roller 19, the developing device 20, the transfer charging roller 21 and the like is performed. To stop. Then, after t4 seconds, the main motor 23 and the polygon motor 15a are stopped, and the normal printing operation is finished.
[0085]
In the continuous print mode, a predetermined number of continuous prints are executed by repeating a cycle in which a predetermined print interval (interval, non-image recording period) is provided after one print operation and the next print operation is executed. When the trailing edge of the last recording sheet S is detected by the paper discharge sensor 11, the temperature control of the ceramic heater 10a of the fixing device 10 is stopped, and the high pressure applied to the primary charging roller 19, the developing device 20, the transfer charging roller 21, and the like. Stop applying drive. Then, after t4 seconds, the main motor 23 and the polygon motor 15a are stopped, and the continuous printing operation is finished.
[0086]
(6) Drive control of main motor 23
FIG. 6 is a circuit diagram of a portion related to the drive control of the main motor 23 of the printer control device 26.
[0087]
A one-chip microcomputer 26a includes a ROM 26b, a RAM 26c, and a timer 26d.
[0088]
The main motor 23 is a four-phase stepping motor, and the windings of the A-phase, / A-phase, B-phase, and / B-phase are connected to the collectors of NPN transistors 31, 32, 33, and 34, respectively. The other is connected to a + 24V power source. The emitters of the NPN transistors 31, 32, 33, and 34 are connected to GND, and the bases are connected to the output ports P0, P1, P2, and P3 of the MPU, respectively. The surge absorbing diode for protecting each NPN transistor is omitted from the drawing.
[0089]
FIG. 7 is a timing chart showing excitation pulses for driving the main motor 23. When rotating the main motor 23, the MPU 26a uses the built-in timer 26d to calculate the frequency of the excitation pulse, and from the output ports P0, P1, P2, P3 at the predetermined frequency, the A phase, / A phase, B phase, / B Outputs phase excitation pulses. Therefore, the rotational speed of the main motor 23 can be changed by changing the frequency of the excitation pulse.
[0090]
That is, if the frequency of the excitation pulse is increased by the printer control device 26, the rotation of the main motor 23 is accelerated and the conveyance speed of the recording paper S is increased. Conversely, if the frequency is lowered, the rotation of the main motor 23 is slowed down, and the conveyance speed of the recording paper S is slowed down.
[0091]
(7) Image stretch correction control
As described above, the pressure roller 10e of the fixing device 10 is heated by the heat from the ceramic heater 10a while continuously performing the printing operation, so that thermal expansion occurs and the outer diameter is larger than the initial diameter. Therefore, as the number of continuous prints (the number of continuous image recordings) increases, the image is extended by pulling and conveying the recording paper S in the transfer unit.
[0092]
In this embodiment, in order to correct this image extension, the printer control device 26 measures the time for which the recording paper S passes a predetermined position (position of the paper feed sensor 7), and the rotation of the main motor 23 based on the time. By controlling the speed, the conveyance speed of the recording paper S is gradually reduced.
[0093]
Specifically, for example, when A4 recording paper S is used, the paper length is 297 mm, and the initial transport speed (conveyance speed when the recording paper S is not pulled by the transfer unit) is 25 mm / s. If there is, the time when the paper feed sensor 7 is turned on, that is, the sensor passage time t5 is 11.88 s.
[0094]
When the recording paper S is pulled and the conveyance speed is high (25.2 mm / s), the sensor passage time t5 is 11.78 s. Therefore, in this example, the rotation speed of the main motor 23 is reduced to suppress the extension of the recorded image.
[0095]
FIG. 8 is a flowchart of the above control.
[0096]
When performing a continuous printing operation, the sensor passage time t5 is first measured, and the measured time is a regular time ( Reference time: For example, it is determined whether it is 0.8% or faster (11.78 s) compared to 11.88 s) (step S1), and if it is 0.8% or faster, the recording paper conveyance speed is set to the initial value. On the other hand, it is reduced by 0.8% (step S2).
[0097]
Next, it is determined whether or not the sensor passage time t5 is further accelerated by 0.8% or more, that is, whether or not the sensor passage time t5 is accelerated by 1.6% or more with respect to the regular time (step S3). If so, the driving speed of the main motor 23 is decreased by 1.6% with respect to the initial speed (step S4).
[0098]
1) That is, when the main motor 23 is driven and controlled to reduce its rotational speed, a recording paper conveyance path from the paper supply roller 5 to the paper discharge roller 12 is formed. 6. The rotational peripheral speeds of the photosensitive drum 18, the transfer charging roller 21, the pressure roller 10e of the fixing device 10 and the paper discharge roller 12 are lower than the normal rotational peripheral speed so that the recording paper transport speed is higher than the normal transport speed. Will also go down.
[0099]
2) Since the rotational peripheral speed of the photosensitive drum 18 is lower than the normal rotational peripheral speed with respect to the latent image forming speed by the exposure means (laser scanner section) 8, the latent image / toner image formed on the photosensitive drum 18 Is formed by being contracted in the photosensitive drum rotating direction by a proportion corresponding to the amount of reduction in the rotational peripheral speed of the photosensitive drum 18.
[0100]
3) Even if the recording paper conveyance speed is lowered by controlling the driving of the main motor 23, the recording paper conveyance speed at the fixing nip N of the fixing device 10 during continuous printing is increased by the thermal expansion of the diameter of the pressure roller 10e. Therefore, the recording paper S is higher than the recording paper conveyance speed in the transfer unit T, and the recording paper S is pulled and conveyed in the transfer unit T.
[0101]
4) Therefore, as in 2) above, the toner image formed on the surface of the photosensitive drum 18 by being contracted in the rotational direction of the photosensitive drum is extended in the recording paper conveyance direction with respect to the recording paper surface pulled and conveyed in the transfer portion T. It will be transcribed.
[0102]
That is, during continuous printing, as shown in the control flowchart above, the main motor 23 corresponds to the increase in the recording paper conveyance speed in the fixing nip portion N due to the increase in the outer diameter based on the thermal expansion of the pressure roller 10e of the fixing device 10. Is controlled to reduce the recording paper conveyance speed by an appropriate ratio, so that the amount of contraction of the toner image formed on the surface of the photosensitive drum 18 is offset from the amount of image extension during transfer, and recording is performed. The corrected toner image is transferred and formed on the paper surface.
[0103]
FIG. 9 is a graph showing the elongation rate of the recorded image and the conveyance speed down rate.
[0104]
As can be seen from this graph, the image extension is suppressed to within 0.8% in the present embodiment.
[0105]
Further, according to the present embodiment, the print image can be extended with a simple configuration without using a mechanism for adjusting the driving speed of only the pressure roller 10e, a special sensor for measuring the recording paper conveyance speed, or the like. Control is achieved.
[0106]
In this embodiment, the recording paper conveyance speed is switched based on the time passing through the paper feed sensor 7. However, the determination is based on the time passing through the paper discharge sensor 11 which is close to the fixing device 10 and is more susceptible. May be. Further, the difference between the time passing through the paper feed sensor 7 and the time passing through the paper discharge sensor 11 (for example, the time from when the trailing edge of the recording paper S is detected by the paper feed sensor 7 until the paper discharge sensor 11 is detected). Whether or not to switch the recording paper conveyance speed may be determined based on the above.
[0107]
In this example, the initial sensor passage time t5 is stored in advance in a ROM or the like for each paper size, for example, and is read from the ROM according to the paper size detected by the paper size sensor 4. In addition, the sensor passage time t5 is measured (for example, measured at the time of printing for a few sheets from the start of printing) in a state where the pressure roller 10e is cooled and stored in the RAM or the like, and this value is obtained during continuous printing. Make reference.
[0108]
In this embodiment, when the sensor passage time t5 reaches a predetermined value, the recording paper conveyance speed corresponding to the value is switched. However, the present invention is not limited to this, and the number of prints when continuous printing is performed is predetermined. It may be possible to measure how much the sensor passage time t5 is faster than the initial value when the number of sheets is reached, and to switch to the recording paper conveyance speed corresponding to the measured value.
[0109]
[0110]
[0111]
[0112]
[0113]
[0114]
[0115]
[0116]
[0117]
[0118]
[0119]
[0120]
[0121]
<Others>
1) By changing the conveyance speed switching timing to the non-exposure time, the change of the magnification within one page can be suppressed to one time.
[0122]
2) The transfer means 21 of the image forming unit can be other means such as a transfer corona charger.
[0123]
3) The image forming unit is not limited to the electrophotographic process of the embodiment, and forms and supports an unfixed image corresponding to target image information on a recording sheet such as an electrostatic recording process or a magnetic recording process by a transfer method or a direct method. Any suitable image forming process means can be used.
[0124]
4) The fixing device 10 is not limited to a type using a ceramic heater, but may be an electromagnetic induction heating type.
[0125]
FIG. (A) and (b) are on-demand type electromagnetic induction heating type fixing devices.
[0126]
FIG. 2A shows a tensionless type / pressure roller driven film heating type apparatus shown in FIG. 2, which is a horizontally long electromagnetic induction heating plate 10h (metal plate, conductor) instead of the ceramic heater 10a as a heating element. , Resistors, magnetic bodies) are arranged on the film inner surface guide stay 10d, and an alternating magnetic field consisting of an excitation coil 10i and an excitation core 10j that causes an alternating magnetic field to act on the electromagnetic induction heating plate 10h inside the guide stay 10d. The magnetic field generating means 10k is provided.
[0127]
The electromagnetic induction heat generating plate 10h functions as a heating element by electromagnetic induction heat generation (heat generation due to eddy current loss) by the action of the alternating magnetic field generated by the alternating magnetic field generating means 10k, and the heat generation rotates as the pressure roller 10e is driven to rotate. The film 10c to be heated is heated at the nip portion N. Then, the recording paper S is introduced between the film 10c and the pressure roller 10e in the nip portion N with the unfixed toner image carrying surface facing the film 10c, so that the recording paper S adheres to the film 10c. Then, the nip portion N is nipped and passed through at a speed corresponding to the rotational peripheral speed of the pressure roller 10e in an overlapping state with the film.
[0128]
In the film heating type apparatus of FIG. 2 which is the tensionless type and pressure roller driving type, the ceramic heater 10a as a heating element is omitted and the film 10c is an electromagnetic induction heat generating film. In addition, an alternating magnetic field generating means 10k including an exciting coil 10i and an exciting core 10j that causes an alternating magnetic field to act mainly on the electromagnetic induction heat generating film portion of the nip portion N is provided inside the film guide 10d.
[0129]
The electromagnetic induction heat generating film 10m generates electromagnetic induction heat mainly in the region of the nip portion N by the alternating magnetic field generated by the alternating magnetic field generating means 10k. Then, the recording paper S is introduced between the film 10m and the pressure roller 10e in the nip portion N with the unfixed toner image carrying surface facing the film 10m, so that the recording paper S adheres to the film 10m. Then, the nip portion N is nipped and passed through at a speed corresponding to the rotational peripheral speed of the pressure roller 10e in an overlapping state with the film.
[0130]
【The invention's effect】
As described above, according to the present invention, the recording paper is conveyed to the image forming unit to form an unfixed image corresponding to the target image information, and the recording paper is removed from the image forming unit. Fixing of pressure roller drive type fixing means Nip Part Introducing unfixed images on recording paper by nipping and conveying heating In the image recording apparatus to be fixed, it is possible to prevent the extension of the recorded image and to reduce the change in the image magnification within one page of the recording paper.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image recording apparatus (laser printer) according to a first embodiment.
FIG. 2 is a schematic configuration diagram of a fixing device (film heating method).
Fig. 3 Schematic diagram of video interface
FIG. 4 is an operation timing chart of serial communication.
FIG. 5 is a timing chart of normal printing operation.
FIG. 6 is a circuit diagram of a motor control part.
FIG. 7 is a diagram showing a stepping motor excitation pattern
FIG. 8 is a flowchart illustrating recording paper conveyance speed control according to the first exemplary embodiment.
FIG. 9 is a graph showing the relationship between the number of continuous prints, the image extension rate, and the recording paper conveyance speed reduction rate.
FIG. 10 (A), (b) is a schematic configuration diagram of another example of a fixing device of a pressure roller driving system / on-demand type
FIG. 11 Graph showing the number of continuous prints and the image extension rate in a conventional image recording apparatus
FIG. Explanatory drawing of the recording image state of each recording sheet of the first output and the 30th continuous recording
[Explanation of symbols]
1 Laser printer (image recording device)
8 Laser scanner section
9 Image forming section
T transcription part
10 Fixing device
10a Ceramic heater (heating body)
10c heat resistant film
10d Film inner surface guide stay
10e Pressure roller (rotating body for pressure conveyance)
23 Main motor
26 Printer control device

Claims (1)

A rotating image carrier, a laser scanner that has a polygon mirror and a polygon mirror driving motor and scans the image carrier according to image information, and a pressure roller that conveys recording paper. In a recording paper conveyance path including a fixing means for nipping and conveying the recording paper carrying the transferred unfixed image at the fixing nip portion to heat and fix the unfixed image on the recording paper, and the image carrier and the pressure roller And a main motor for driving all the recording paper conveying members , and the distance between the image transfer position from the image carrier to the recording paper and the fixing nip portion is at least one size that can be used in the apparatus In an image recording apparatus shorter than the paper transport direction size ,
Controls the measuring means for measuring the time for a sheet of recording paper that is nipped and conveyed at the fixing nip portion to pass a predetermined position in the recording paper conveyance path, and controls the main motor and the polygon mirror driving motor. And a control unit that drives the polygon mirror when a measurement time required for a sheet of recording paper to pass the predetermined position becomes shorter than a reference time required for the recording sheet to pass the predetermined position. It driving speed of use the motor without changing overlooked the driving speed of the main motor, the magnification of the image bearing member rotational direction of the image formed on the image bearing member reduces from the reference ratio by the driving speed down the main motor The magnification in the recording paper conveyance direction of the image transferred onto the recording paper at the image transfer position is caused by the pulling of the recording paper due to the increase in the recording paper conveyance speed of the fixing nip portion. Image recording apparatus, characterized in that to suppress the Enlarge quasi magnification.