JPH08142431A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To always achieve proper feed control regardless of the size of a recording medium by detecting the rotation difference of a feed means to accurately detect that the recording medium is passed through an upstream feed means and changing over the feed speed of a downstream feed means from high speed rotation to low speed rotation. CONSTITUTION: When the feed of recording paper P is started, since the recording paper P is held only by a lower feed roller pair 3 at first, a speed changeover clutch 6 is turned ON and an upper feed roller pair 4 is driven at a high speed. When the rear end of the recording paper P comes out of the lower feed roller pair 3, the recording paper P is fed only by the upper feed roller pair 4 held to a high speed state and, therefore, an energizing roller 8b is rotated at a high speed. At this time, a difference is generated between the respective output signals of the encoder 9 for the energizing roller and the encoder 10 for the feed rollers. When the output difference is not detected, the energizing roller 8b is continuously rotated at a high speed and, when the output difference is detected, the speed changeover clutch 6 is turned OFF.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a facsimile, a copying machine,
The present invention relates to an image forming apparatus such as a printer, and more particularly to an image forming apparatus which forms an image while sandwiching and transporting a recording medium between first and second transporting means.

[0002]

2. Description of the Related Art An example of a conventional image forming apparatus will be described with reference to FIG. FIG. 8 is a configuration diagram of an image recording unit and a recording medium conveying unit of an image forming apparatus that forms an image by serial scanning using a recording head of an inkjet recording system as a recording head.

In FIG. 8, a recording sheet P is a manual sheet feeding port.
The paper is fed from 51 and conveyed by the manual feed roller pair 52 toward the lower conveyance roller pair 53. The lower conveyance roller pair 53 is driven by the conveyance motor 55 via the conveyance roller drive belt 54, and the recording paper P is conveyed to the upper conveyance roller pair 56. The upper carrying roller pair 56 is driven by a carrying motor 55 via a carrying roller driving belt 57 and a speed switching clutch 58. When the speed switching clutch 58 is turned on, the drive of the carry motor 55 is transmitted to the upper carry roller pair 56 via a pulley having a small diameter, and the high speed rotation is performed. When the speed switching clutch 58 is turned off, the pulley is switched to a larger diameter, and the upper conveying roller pair 56 rotates at a low speed.

Here, high speed rotation means a pair of upper conveying rollers 56.
Is rotated at a higher speed than the lower conveyance roller pair 53, and the recording paper P is conveyed by being pulled by the upper conveyance roller pair 56. Since the pressure with which the upper conveyance roller pair 56 clamps the recording sheet P is smaller than the pressure with which the lower conveyance roller pair 53 clamps the recording sheet P, when the conveyance is performed in such a manner, the conveyance amount is lower. The upper conveyance roller pair 56 slides as determined by the conveyance amount of 53. In such a pulling conveyance, since the conveyance amount is determined by the conveyance amount of the paper before recording, the conveyance amount does not affect the recording density and can be stably conveyed.

The low speed rotation means a case where the upper conveying roller pair 56 rotates at the same speed as the lower conveying roller pair 53 to convey the recording paper P. After the recording paper P has passed through the lower conveyance roller pair 53, it is conveyed by the upper conveyance roller pair 56 at such a low speed. Whether or not the recording paper P has passed through the lower conveyance roller pair 53 is determined by detecting the passage of the sheet edge by the paper sensor 59 arranged near the lower conveyance roller 53.

The recording head 60 also serially cancels on the platen 61 that supports the recording paper P, and ejects ink according to image information to form an image for one line corresponding to the head width. After the image formation, the recording paper P is the above-mentioned upper conveyance roller pair 56.
And the lower conveyance roller pair 53 conveys the recording head by the width of the recording head. An image is formed by alternately repeating the recording scan and the recording paper conveyance.

The switching timing of the speed switching clutch 58 of the pair of upper transport rollers 56 depends on the size of the recording paper which is known in advance, and is set to a lower value after the rear end of the paper passes the paper sensor 59 from the transport amount of the paper. The position at which the conveying roller pair 53 exits is calculated and determined.

[0008]

However, in the above-mentioned prior art, since the switching timing of the speed switching clutch 58 is calculated from the paper size and the carry amount, it cannot be applied when the paper is non-standard. Even though the recording paper P has passed through the lower conveyance roller pair 53,
If the upper conveyance roller pair 56 is kept rotating at a high speed, the amount of conveyance is too large and white streaks occur.

The paper sensor 59 can also detect the trailing edge of the recording paper, but since there is a gap between the paper sensor 59 and the lower conveyance roller pair 53, and the amount of conveyance differs depending on the recording state, the paper sensor 59 records. The calculation of the timing when the sheet actually passes through the lower conveyance roller pair 53 after detecting the trailing edge of the sheet becomes complicated.

An object of the present invention is to solve the above-mentioned problems of the prior art, to accurately detect the timing at which a recording medium passes through the first conveying means on the upstream side of the image forming means, and to detect the timing on the downstream side of the image forming means. An object of the present invention is to provide an image forming apparatus capable of providing a high-quality image in a stable manner by appropriately adjusting the timing of switching the transport speed of the second transport means.

[0011]

A typical means for solving the above problems of the prior art and applied to the embodiments described below is an image forming means for forming an image on a recording medium according to image information, A first conveying unit arranged upstream of the image forming unit in the recording medium conveying direction; a second conveying unit arranged downstream of the image forming unit in the recording medium conveying direction and having a variable conveying speed; A driving means for driving the second conveying means, and a detecting means for detecting whether or not the first conveying means is conveying a recording medium. (2) The carrying speed of the carrying means is switched.

[0012]

According to the above means, the detecting means is, for example,
By detecting the rotation difference of the second conveying means, it is accurately detected that the recording medium has passed the first conveying means on the upstream side of the image forming means, and the second conveying means on the downstream side of the image forming means. The conveyance speed of is switched from high speed rotation to low speed rotation.

[0013]

【Example】

[First Embodiment] Next, an embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. In this embodiment, an ink jet recording apparatus will be used for description. FIG. 1 is a cross-sectional explanatory view showing a schematic configuration of an inkjet recording apparatus, FIG. 2 is a block diagram showing a configuration of a control system of a sheet conveying unit of the inkjet recording apparatus, and FIG. 3 is a flowchart showing speed switching timing.

First, a schematic structure of an ink jet recording apparatus will be described with reference to FIG. In FIG. 1, a recording sheet P as a recording medium is conveyed from the lower side to the upper side in the figure. Reference numeral 1 denotes a recording head as an image forming unit, which records an ink image on a recording sheet P conveyed by a conveying unit described later according to a signal based on image information. As a recording means in this apparatus, an inkjet recording method is used in which ink is ejected from a recording head to perform recording. That is, this recording head has a fine liquid discharge port (orifice), a liquid passage and an energy acting portion provided in a part of this liquid passage, and energy generation for generating droplet forming energy for acting on the liquid in the acting portion. Equipped with means.

As the energy generating means for generating such energy, a recording method using an electromechanical transducer such as a piezo element is used, electromagnetic waves such as laser are irradiated to generate heat, and droplets are ejected by the action of the heat generation. There are a recording method using an energy generating means, a recording method using an energy generating means for heating a liquid and discharging the liquid by an electrothermal converter such as a heating element having a heating resistor.

Among them, a recording head used in an ink jet recording method for ejecting a liquid by thermal energy has a high density of liquid ejection ports (orifices) for ejecting recording liquid droplets to form ejection liquid droplets. Since they can be arranged, high resolution recording is possible. Among them, the recording head using the electrothermal converter as the energy generating means can easily be made compact, and has the advantages of the IC technology and the microfabrication technology, which have been remarkably improved in technology and reliability in the recent semiconductor field. This is advantageous because it can be used in two parts, high-density mounting is easy, and the manufacturing cost is low.

The recording head 1 records on the recording paper P supported by the platen 2 by the width of the head while serially scanning in the main scanning direction (the direction perpendicular to the drawing) by a driving means (not shown).

A lower conveying roller pair 3 as a first conveying means is arranged upstream of the recording head 1 in the sheet conveying direction. Reference numeral 4 denotes an upper conveying roller pair as a second conveying means, which is arranged downstream of the recording head 1 in the sheet conveying direction. The recording paper P is conveyed while being sandwiched by the lower conveyance roller pair 3 and the upper conveyance roller pair 4. The lower conveyance roller pair 3 and the upper conveyance roller pair 4 are composed of a drive-side roller to which drive is transmitted and a driven-side roller pressed against the drive-side roller.

A conveying motor 5 is a driving means, and the lower conveying roller pair 3 is driven by the conveying motor 5 via a conveying roller driving belt 3a. The upper conveying roller pair 4 is driven by a conveying motor 5 via a speed switching clutch 6 and a conveying roller driving belt 7.

When the speed switching clutch 6 is turned on, the upper conveying roller pair 4 is driven at a speed several percent higher than the lower conveying roller pair 3, and the recording paper P is conveyed so as to be pulled by the upper conveying roller pair 4. At this time, the pressure with which the upper conveying roller pair 4 sandwiches the recording sheet P is smaller than the pressure with which the lower conveying roller pair 3 sandwiches, so that if the sheet is conveyed by pulling, the recording sheet P slips at the nip portion of the upper conveying roller pair 4. Therefore, the carrying amount is determined by the lower carrying roller pair 3. When the speed switching clutch 6 is turned off, the upper conveyance roller pair 4
Is driven at the same speed as the lower conveying roller pair 3.

A roller pair 8 for sandwiching the recording paper P and being driven is provided on the downstream side of the upper conveying roller pair 4.
The roller 8a and a biasing roller 8b that presses the roller 8a and follows the roller 8a are provided. The urging roller 8b is a roller that urges the recording paper P to rotate, and the rotation speed of the urging roller 8b is detected by an urging roller encoder 9 as a detecting means connected via a belt. It The number of rotations of the drive roller on the drive side of the lower transport roller pair 3 is detected by the transport roller encoder 10 as a detection means connected via a belt.

The block diagram of FIG. 2 shows the configuration of the control system of the paper transport unit of the above-mentioned ink jet recording apparatus. In FIG. 2, the output signals of the urging roller encoder 9 and the conveying roller encoder 10 are input to the rotation detection unit 11. The rotation detection unit 11 detects the rotation difference between the upper conveyance roller pair 4 and the lower conveyance roller pair 3 based on the input signals of both the encoder 9 and the encoder 10. Reference numeral 12 denotes a CPU, which controls the conveying operation of the recording paper P according to the program of the program ROM 13. The RAM 14 also includes a working area in which the CPU 12 temporarily stores the data in the instruction and the operation result, a buffer area in which the data input from the outside is stored. When the CPU 12 receives a signal from the rotation detection unit 11, the CPU 12 controls the drive of the transport motor 5 that transports the recording paper P via the motor drive unit 15.

Next, the timing of speed switching by the control system of the above-mentioned sheet conveying section will be described with reference to the flow chart shown in FIG. When the conveyance of the recording paper P is started,
In step S1, since it is initially sandwiched only by the lower conveying roller pair 3, the speed switching clutch 6 is kept ON and the upper conveying roller pair 4 is driven at high speed. However, since the recording paper P is transported by the transport amount defined by the lower transport roller pair 3, the output signals (the output pulse numbers) of the urging roller encoder 9 and the transport roller encoder 10 are equal.

When recording by the recording head 1 progresses and the trailing edge of the recording sheet P passes through the lower conveying roller pair 3, the recording sheet P is conveyed only by the upper conveying roller pair 4 in the high speed state, and therefore the urging force is applied. The roller 8b rotates at high speed. At this time, a difference occurs between the output signals of the energizing roller encoder 9 and the conveying roller encoder 10. In step S2, it is determined whether or not the rotation detection unit 11 has detected a difference in output. When the output difference is not detected, the urging roller 8b continues to rotate at high speed, and when the rotation detection unit 11 detects the output difference, the CPU 12 proceeds to step S3 and sets the speed switching clutch 6 to OFF.
F As a result, the upper conveying roller pair 4 conveys the recording paper P at the same speed as the lower conveying roller pair 3, and the conveying speed becomes appropriate. Further, the speed difference between the upper conveying roller pair 4 rotating at a high speed and the lower conveying roller pair 3 is several%, and even if the speed switching clutch 6 is switched after detecting the speed difference, the influence on the image is affected. Is few. Since the control of the speed switching clutch 6 is performed asynchronously with the conveyance control of the recording paper P, even if the recording paper P has a non-standard size, proper conveyance control is performed without any problem.

According to the above structure, when it is detected that the recording paper P has passed through the lower conveying roller pair 3 on the upstream side of the recording head 1, the conveying speed of the upper conveying roller pair 4 on the downstream side of the recording head 1 is increased. By switching from the low speed to the low speed, it is possible to properly control the conveyance of the recording paper regardless of the paper size, and it is possible to stably provide a high-quality image.

[Second Embodiment] Another example of the ink jet recording apparatus will be described with reference to FIGS. 4 and 5. Since the schematic configuration of the ink jet recording apparatus is the same as that of the first embodiment, the same members are designated by the same reference numerals, and the description thereof is cited. The characteristic points will be mainly described below.

In this embodiment, the number of drive pulses of the urging roller encoder 9 and the conveyance motor 5 is compared to detect that the recording paper P has passed through the lower conveyance roller pair 3 in FIG. That is, in FIG. 5, the carry motor 5 is a pulse motor, and the motor drive unit 15 outputs a carry motor driving pulse signal. The encoder output from the energizing roller encoder 9 and the carry motor driving pulse signal are input to the pulse frequency difference detection unit 16. The pulse frequency difference detector 16 detects the frequency difference between two input pulse signals.

At the start of recording, the speed switching clutch 6 is switched to the high speed side, and as described above, the recording paper P
The transport speed of is defined by the transport speed of the lower transport roller pair 3. When the recording sheet P passes through the lower conveying roller pair 3, the recording sheet P is conveyed at the conveying speed of the upper conveying roller pair 4, that is, at a high speed, so that the conveying motor driving pulse signal and the urging roller encoder 9 are used. The frequency difference between the output pulse signals of 1 becomes larger. The pulse frequency difference detector 16 detects the frequency difference between the two input pulse signals, and when the frequency difference exceeds a certain level, the CPU 12 determines that the recording paper P has passed through the lower conveyance roller 3, and the speed switching clutch 6 is activated. Switch to the constant speed side.

Also with the above-mentioned structure, it is possible to perform the appropriate transport speed control according to the paper size.

[Third Embodiment] Next, another example of the ink jet recording apparatus will be described with reference to FIGS. 6 and 7. Since the schematic configuration of the ink jet recording apparatus is the same as that of the first embodiment, the same members are designated by the same reference numerals, and the description thereof is cited. The characteristic points will be mainly described below.

In FIG. 6, the lower conveying roller pair 17 is provided with a driving roller 17a and a driven roller 17b which is pressed and driven by the driving roller 17a, and the rotation shaft of the driven roller 17b is movable in the direction perpendicular to the axial direction. Supported and roller presser spring 18
It is pressed by the drive roller 17a side. Reference numeral 19 denotes a roller position displacement sensor, which detects the position displacement of the driven roller 17b. Therefore, when the recording sheet P passes through the lower conveying roller pair 17, the driven roller 17b is displaced in the direction perpendicular to the axial direction by the thickness of the recording sheet P against the urging force of the roller pressing spring 18. By detecting the displacement amount by the roller position displacement sensor 19,
It can be detected that the recording paper P has passed through the lower conveyance roller pair 17.

As shown in FIG. 5, the output of the roller position displacement sensor 19 is input to the roller position detection unit 20 and the CPU
Reference numeral 12 determines whether or not the recording sheet P has passed through the lower conveyance roller pair 17 based on the output of the roller position detection unit 20. After passing through the lower conveyance roller pair 17, the speed switching clutch 6 is moved from the high speed side to the constant speed side. Switch to.

As described above, the position displacement of the driven roller 17b is detected by the roller position displacement sensor 19 to determine whether the lower conveyance roller pair 17 is conveying the recording paper P, and the speed switching clutch is detected according to the output of the sensor. By switching 6 it is possible to properly control the conveyance speed of the recording paper P.

Further, although the ink jet recording system is used as the recording means in the above-mentioned first to third embodiments, the electrothermal converter is energized according to a recording signal and the thermal energy applied by the electrothermal converter is used. It is more preferable that the recording is performed by ejecting the ink from the ejection port due to the growth and contraction of the bubbles generated in the ink by utilizing the film boiling generated in the ink.

This system can be applied to both the so-called on-demand type and the continuous type, but in the case of the on-demand type in particular, it corresponds to the sheet or the liquid path holding the liquid (ink). To the electrothermal converter that is arranged as
By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding nucleate boiling, heat energy is generated in the electrothermal converter, and film boiling occurs on the heat acting surface of the recording head. This is effective because bubbles can be formed in the liquid corresponding to this drive signal one-to-one as a result. Due to the growth and contraction of the bubbles, the liquid is ejected through the ejection openings to form at least one droplet. It is more preferable to make this drive signal into a pulse shape, because the bubble growth and contraction are immediately and appropriately performed, so that particularly excellent liquid ejection can be achieved.

Further, the present invention can be effectively applied to a full-line type recording head having a length corresponding to the maximum width of a recording medium which can be recorded by the recording apparatus. Such a recording head may have a structure that satisfies the length by combining a plurality of recording heads or a structure as one recording head integrally formed.

In addition, even in the case of the serial type described above, it is possible to electrically connect to the apparatus main body and supply ink from the apparatus main body by mounting the recording head fixed to the carriage or the carriage. A replaceable chip type recording head or a cartridge type recording head in which an ink tank is integrally provided in the recording head itself may be used.

Further, it is preferable to add recovery means for the recording head, preliminary auxiliary means, etc., which are provided as a component of the image forming apparatus of the present invention, because the effects of the present invention can be further stabilized. Specific examples of these are capping means for the recording head, cleaning means,
Pressurization or suction means, electrothermal conversion type or other heating element or a preheating means with a combination of these, predischarge mode for discharging other than recording is also effective for stable recording. Is.

Regarding the type or number of recording heads mounted on the carriage, for example, only one is provided corresponding to a single color ink, or a plurality of inks having different recording colors and densities are supported. And a plurality of them may be provided. That is, for example, the recording mode of the recording apparatus is not limited to a recording mode of only the mainstream color such as black, but may be a combination of a plurality of recording heads integrally formed, but a mixed color of different colors or a mixed color It is also applicable to a device with at least one of the full colors according to

In addition, in the above-mentioned embodiments, the ink is described as a liquid, but it is an ink which solidifies at room temperature or lower and softens or liquefies at room temperature, or in the ink jet recording system. 30 inks
Generally, the temperature is controlled in the range of ℃ to 70 ℃ to control the temperature of the ink so that the viscosity of the ink is within the stable ejection range. good. In addition, it is possible to prevent the temperature rise due to thermal energy from being positively used as the energy for changing the state of the ink from the solid state to the liquid state, or to use ink that solidifies when left standing for the purpose of preventing ink evaporation. However, in any case, when heat ink is liquefied by applying heat energy according to the recording signal and liquid ink is ejected, or when the ink reaches the recording sheet, it begins to solidify. It is also applicable when using an ink that has the property of being liquefied for the first time by energy.

Further, as the form of the above-mentioned ink jet recording device, in addition to the form used as an image output terminal of an information processing device such as a computer, a form of a copying device combined with a reader or the like, and a form of a facsimile device having a transmitting / receiving function. It may be something to take.

Although an example using the ink jet recording system as the image forming means has been described, the present invention is not limited to the ink jet recording system, and the recording system is not limited to the ink jet recording system.
In addition, a thermal transfer recording method, a thermal recording method, and a recording method other than the impact recording method such as a wire dot recording method can be applied. Further, it is not necessary to limit to the serial recording method, and a so-called line recording method may be used.

[0043]

As described above, according to the present invention, the recording medium passes through the first conveying means on the upstream side of the image forming means by detecting the rotation difference between the first and second conveying means by the detecting means. By accurately detecting that, by switching the transport speed of the second transport unit downstream of the image forming unit from high speed rotation to low speed rotation, proper transport control can be performed regardless of the size of the recording medium, It is possible to stably provide a high-quality image.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view showing a schematic configuration of an inkjet recording apparatus according to a first embodiment.

FIG. 2 is a block diagram showing a configuration of a control system of a paper transport unit.

FIG. 3 is a flowchart showing timing of speed switching.

FIG. 4 is a cross-sectional explanatory view showing a schematic configuration of an inkjet recording apparatus according to a second embodiment.

FIG. 5 is a block diagram showing a configuration of a control system of a paper transport unit.

FIG. 6 is a cross-sectional explanatory diagram showing a schematic configuration of an ink jet recording apparatus according to a third embodiment.

FIG. 7 is a block diagram showing a configuration of a control system of a paper transport unit.

FIG. 8 is an explanatory diagram showing a schematic configuration of a conventional inkjet recording apparatus.

[Explanation of symbols]

 P ... Recording paper 1 ... Recording head 2 ... Platen 3 ... Lower transport roller pair 3a, 7 ... Transport roller drive belt 4 ... Upper transport roller pair 5 ... Transport motor 6 ... Speed switching clutch 8 ... Roller pair 8a ... Roller 8b ... Attached Energizing roller 9 ... Energizing roller encoder 10 ... Conveying roller encoder 11 ... Rotation detecting unit 12 ... CPU 13 ... ROM 14 ... RAM 15 ... Motor driving unit 16 ... Pulse frequency difference detecting unit 17 ... Lower conveying roller pair 17a ... Driving Roller 17b ... Driven roller 18 ... Roller pressing spring 19 ... Roller position displacement sensor 20 ... Roller position detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B65H 43/00 G03G 21/14

Claims (7)

[Claims] 1. An image forming unit for forming an image on a recording medium according to image information, a first conveying unit arranged upstream of the image forming unit in a recording medium conveying direction, and a recording medium for the image forming unit. A second conveying unit arranged on the downstream side in the conveying direction and having a variable conveying speed, a driving unit for driving the first and second conveying units, and detecting whether or not the first conveying unit is conveying the recording medium. An image forming apparatus, comprising: a detection unit for controlling the conveyance speed of the second conveyance unit driven by the drive unit according to a detection result of the detection unit. 2. The image forming apparatus according to claim 1, wherein the detection unit detects a rotation difference between the first and second conveyance units. 3. The image forming apparatus according to claim 1, wherein the detection unit detects a pulse frequency difference between the driving pulse number of the driving unit and the rotation number of the second conveying unit. 4. The image forming apparatus according to claim 1, wherein the detection unit detects a positional displacement of a roller forming the second conveyance unit. 5. The image forming apparatus according to claim 1, wherein the image forming unit is an ink jet recording system that performs recording by ejecting ink in accordance with a signal based on image information. 6. The image forming apparatus according to claim 5, wherein the image forming unit includes an electrothermal converter for generating thermal energy for ejecting ink. 7. The image forming unit causes the ink to be ejected from an ejection port by utilizing the film boiling generated in the ink by the thermal energy applied by the electrothermal converter. Image forming apparatus.