JPH05138900A - Image forming device - Google Patents

Abstract

PURPOSE:To enable shift in registration by time-sharing drive to be minimized by a method wherein a drive power source is reduced by time-shared driving of a plurality of recording heads to provide a low cost image forming device. CONSTITUTION:An image data signal VD is separated per each color to be taken into a delay memory 57 existing in a recording head drive part (52-54) for each color. Thus taken each color image data is made to be a parallel data with a shift register 58 to be transmitted to a head driver via a latch 59. A head drive pulse instructing its drive timing is inputted to a head driver from a timing generation part 51. Then, ON/OFF control for supply of a current to each heating element 502 of a recording head 503 is executed with the abovementioned parallel image data and the head drive pulse. Correction of registration is executed by an order of the head drive pulse and alteration of the timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a plurality of recording heads and forming recording images by successively superimposing recording dots from the respective recording heads.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type, for example, a color printer apparatus using a plurality of ink jet heads, has an independent driving power source for each of a plurality of ink jets. The misregistration (registration) of printing between the heads is configured so that a clock frequency several times faster than the pixel clock is counted, and the print start timing is obtained from the counted value.

[0003]

However, having an independent driving power source for each ink jet head as in the above-mentioned conventional example can adjust registration with high accuracy, but is disadvantageous in terms of cost. There was a drawback that it was expensive.

The present invention has been made in view of the above problems, and provides a low-priced image forming apparatus capable of driving a plurality of recording heads in a time-division manner, reducing the driving power source.
Also, by making it possible to set which recording head is assigned to the drive timing of each divided recording head,
An object of the present invention is to provide an image forming apparatus capable of minimizing registration deviation due to time division driving.

[0005]

In order to achieve the above object, an image forming apparatus according to the present invention has a plurality of recording heads, and the recording dots from the recording heads are sequentially overlaid to form an image. The image forming apparatus to be formed is provided with recording head driving means for driving the recording heads so that the driving timings of the recording heads do not overlap.

Further, the above-mentioned configuration further comprises drive order changing means for changing the order of the drive timings of the recording heads.

Further, the above structure further comprises timing changing means for changing each driving timing of each recording head.

[0008]

In the above structure, since a plurality of recording heads are driven in a time division manner, the recording head driving power source is reduced. Further, the registration correction by time-division driving is performed by changing the driving order of the recording heads. Further, the registration correction is performed with higher accuracy by changing the drive timing of the recording head.

[0009]

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is an external perspective view of a digital color copying machine to which the present invention is applied. The upper part is a color image scanner 1 which reads a document image and outputs digital color image data to an external device. The lower part is a printer unit 3 for recording a color digital image signal output from the color image scanner 1 on a recording sheet.
In this embodiment, the printer unit 3 is disclosed in Japanese Patent Laid-Open No. 54-5993.
It is a full-color inkjet printer using the recording head of the inkjet recording system described in Japanese Patent Laid-Open No.
The upper and lower parts described above are separable, and can be installed at distant places by extending the connection cable.

FIG. 2 is a side sectional view of the digital color copying machine of FIG. First, the exposure lamp 14 and the lens 1
5. An image of a document placed on the platen glass 17 by an image sensor 16 (a CCD image sensor in this embodiment) capable of reading a line image in full color, a projected image by a projector or a sheet document image by a sheet feeding mechanism 12. read. Next, the controller unit 2 in the scanner unit 1 performs various kinds of image processing on the read image, and the printer unit 3 records the image on recording paper based on the image data from the controller unit 2.

Next, the printer section 3 will be described. In FIG. 2, the recording paper is supplied by a paper feed cassette 20 for storing cut sheets of a small standard size (A4 to A3 in this embodiment) and a large size (A2 to A in this embodiment).
Roll paper 29 for recording up to one size is used. Further, as for the paper feeding, by inserting the recording papers one by one from the manual feeding port 32 of FIG. 2 along the paper feeding unit cover 21,
Paper feeding from outside (manual feeding) is also possible.

The pick-up roller 24 is a roller for feeding the cut sheets one by one from the paper cassette 20, and the fed cut sheets are the cut sheet feeding roller 25.
Is conveyed to the first paper feed roller 26.

The roll paper 29 is sent out by a roll paper feed roller 30, cut into a standard length by a cutter 31, and conveyed to the paper feed first roller 26.

Similarly, the recording sheet inserted through the manual feed port 22 is conveyed to the first paper feed roller 26 by the manual feed roller 32.

The pick-up roller 24, the cut paper feed roller 25, the roll paper feed roller 30, the first paper feed roller 26, and the manual feed roller 32 are a feed motor (not shown) (in this embodiment, a DC servo motor). Is used), and the on / off control can be performed at any time by an electromagnetic clutch attached to each roller.

When the printing operation is started by an instruction from the controller unit 2, the recording paper which is selectively fed from one of the above-mentioned paper feed paths is conveyed to the first paper feed roller 26. In order to remove the skew of the recording paper, after forming a predetermined amount of paper loop, the first paper feed roller 26 is turned on to convey the recording paper to the second paper feed roller 27.

Paper feed first roller 26 and paper feed second roller 27
In the interval, in order to perform an accurate paper feeding operation between the paper feeding roller 28 and the second paper feeding roller 27, the recording paper is slackened by a predetermined amount to form a buffer. Buffer amount detection sensor 33
Is a sensor for detecting the buffer amount. By constantly making the buffer during conveyance, it is possible to reduce the load on the paper feed roller 28 and the second paper feed roller 27, especially when a large-sized recording paper is conveyed, and it is possible to perform an accurate paper feed operation. ..

When printing with the recording head 37,
The scanning carriage 34, on which the recording head 37 and the like are mounted, reciprocally scans on the carriage rail 36 by the scanning motor 35. Then, in the forward scan, an image is printed on the recording paper, and in the backward scan, the paper feed roller 28 feeds the recording paper by a predetermined amount. At this time, while the drive system is detected by the buffer amount detection sensor 33 by the paper feed motor, control is performed so that the predetermined buffer amount is always obtained.

The printed recording paper is output to the paper output tray 23.
To complete the printing operation.

Next, referring to FIG. 3, the scanning carriage 34 is used.
Give a detailed explanation of the surroundings.

In FIG. 3, a paper feed motor 40 is a drive source for intermittently feeding the recording paper, and the paper feed roller 2
8. The sheet feeding second roller 27 is driven via the sheet feeding second roller clutch 43.

The scanning motor 35 has a drive limit for scanning the scanning carriage 34 in the directions of arrows A and B via the scanning belt 42. In this embodiment, pulse motors are used as the paper feed motor 40 and the scanning motor 35 because accurate paper feed control is required.

When the recording paper reaches the second paper feed roller 27, the second paper feed roller clutch 43 and the paper feed motor 40.
Is turned on, and the recording paper is fed to the paper feed roller 28 to the platen 39.
Carry on top.

The recording paper is detected by a paper detection sensor 44 provided on the platen 39, and the sensor information is used for position control, jam control and the like.

When the recording paper reaches the paper feed roller 28,
The second paper feed roller / clutch 43 and the paper feed motor 40 are turned off, and a suction motor (not shown) performs a suction operation from the inside of the platen 39 to bring the recording paper into close contact with the platen 39.

Prior to the image recording operation on the recording paper, the scanning carriage 34 is placed at the position of the home position sensor 41.
Next, forward scanning is performed in the direction of arrow A, and cyan, magenta, yellow, and black inks are ejected from a predetermined position from the recording head 37 to perform image recording. When the image recording for the predetermined length is completed, the scanning carriage 34 is stopped, and conversely, the backward scanning is started in the direction of the arrow B to reach the position of the home position sensor 41.
Bring back. During the backward scan, the paper feed motor 40 feeds the paper by the length recorded by the recording head 37.
The recording paper is conveyed in the direction of arrow C by driving.

In the present embodiment, the recording head 37 is an ink jet nozzle of the type that forms bubbles by heat and ejects ink droplets at the pressure, and it has four nozzles each having 256 nozzles assembled therein. I'm using a book.

The scanning carriage 34 is at the home position.
When it stops at the home position detected by the sensor 41, the recovery operation of the recording head 37 is performed. This is a process for performing a stable recording operation, and in order to prevent unevenness at the start of ejection, which is caused by a change in the viscosity of the ink remaining in the nozzles of the recording head 37, the paper feeding time, the temperature inside the apparatus, and the like. , A process of performing a pressurizing operation on the recording head 37, an idle ejection operation of ink, and the like according to pre-programmed conditions such as ejection time.

By repeating the operation described above, an image is recorded on the entire surface of the recording paper.

Next, the ink ejection timing of these recording heads 37 will be described. FIG. 4 is a diagram illustrating the timing of one of the recording heads 37. The main scanning direction of FIG. 4 is the scanning direction described above (see FIG.
Direction A).

VE and BVE are signals generated by a controller (not shown), and VE is 25 of the recording head 37.
It is a signal indicating the recording timing of one line of 6 pixels. This VE signal is continuously generated by the number of recording pixels in the main scanning direction to form an image. The image data signal corresponding to each nozzle is synchronized with the VE signal, and the number of nozzles of all the recording heads 37 (256 nozzles × 4 in this embodiment) is sent in one VE section. The BVE signal is a section signal indicating the recording length in the main scanning direction, and the VE signal is valid only during one BVE section. Needless to say, VE and BVE are controlled and generated by a controller (not shown) so that the VE and BVE can be accurately printed according to the size of the recording paper.

FIG. 5 is a block diagram showing a method of controlling the recording head 37, and FIG. 7 is a timing diagram for explaining the timing of FIG. In FIG. 5, blocks 52, 53, 54, and 55 are print head drive units for cyan (C), magenta (M), yellow (Y), and black (BK), respectively, and the four blocks are exactly the same. It has a circuit configuration. Reference numeral 51 denotes a timing generation block, which is a transfer clock VCLK for image data and VE described above.
A timing pulse for the recording head is generated from each BVE signal.

VD in FIG. 5 is image data, and as shown in FIG. 7, C0, M0, Y0 and Bk0 are synchronized with VCLK.
, C1, M1, ... are serially transferred for each color. Further, the timing generation block 51 outputs write pulses CWRCLK and MWR to the delay memory 57.
CLK, YWRCLK, BKWRCLK are generated. Then, the above-mentioned image data VD is separated and written for each color in the delay memory 57 of each recording head drive section (52 to 55) by each of the above-mentioned write pulses. That is, cyan data is stored in the delay memory 57 of the recording head drive unit 52,
Magenta data is separately written to the delay memory 57 of the print head drive unit 53, yellow data is written to the delay memory 57 of the print head drive unit 54, and black data is written to the delay memory 57 of the print head drive unit 55.

The delay memory 57 is a known FIFO memory, and is for correcting (registering) the amount of misalignment of printing depending on the arrangement interval between the recording heads 37 shown in FIG. The image data written in the delay memory 57 is read by a controller CPU (not shown) after a preset delay time has elapsed.

CRDCLK of the delay memory 57 of FIG. 5 is the read clock for cyan. As shown in FIG. 7, C
RDCLK has a cycle of 1/4 of VCLK. Further, although only the CRDCLK is shown in FIG. 7, the RDCLKs for the other three colors have different delay times.
It has the same cycle as CLK. The delay time is set to n × VE cycles (n is an integer) with one cycle of the VE signal as a reference unit.

The image data read from the delay memory 57 by the above-mentioned read clock is serially input to the shift register 58. The shift register 58 has the same number of bits as the number of nozzles of the recording head, and has 256 bits in this embodiment. The image data sequentially input to the shift register 58 and shifted is 2
When all 56 bits have been shifted and input, the parallel output terminal moves to the latch 59 by a CLATP pulse,
It is parallel data for one head. This state is as shown in the timing chart of FIG.

A recording head 503 in FIG.
Is a heating resistor corresponding to one nozzle. The head drive power supply 56 is a head drive pulse (CHDR
A current is supplied to the heating resistor 502 via the head driver 501 at the timing of P). The current supply to the heating resistor 502 is ON / OFF controlled for each heating resistor 501 based on the image data latched by the latch 59.

Next, a method of driving the recording head will be described with reference to FIGS. 6 and 8. FIG. 6 is a circuit included in the timing generation block 51 of FIG. 5 and shows a circuit for generating a head drive signal.

The drive pulse generator 60 shown in FIG.
Is a block that generates pulses corresponding to HDRP0 to HDRP3. The generated drive pulse is 61 in the next stage.
.. to 64 select which of HDRP0 to HDRP3 to use. For example, which of HDRP0 to HDRP3 is used as the cyan drive pulse (CHDRP) is selected by the drive pulse setting signal to the S0 and S1 terminals of the selector 61. This selection circuit
It is provided for each color of C, M, Y, BK,
It is given as a drive pulse setting signal from a CPU mounted on a controller (not shown). And this one
One drive pulse drives all the nozzles of one recording head (256 nozzles in this embodiment).

In this way, the drive pulse is time-divided so that only one recording head 37 is driven at the same timing, so that the head drive power supply 56 can drive all nozzles of one recording head. It only needs to have a current capacity.

To determine which drive pulse is to be assigned to each of the four colors of C, M, Y, and BK, a predetermined test pattern (not shown) is actually printed, and the color shift between the four colors (hereinafter referred to as registration) is visually checked. It is decided by inspecting by, and selecting the combination that minimizes the deviation. This setting data is stored in a non-volatile memory in the controller (not shown) and is reset by the CPU (not shown) when the power is turned on.

The registration adjustment is performed so that when the adjustment is maximized, the yellow color, then the black color, and then the magenta color are located at the most displaced position with respect to the cyan print dot. This is because the yellow color is the most inconspicuous, so even if the registration is somewhat poor, it is not so noticeable. Cyan and magenta are conspicuous, so set them so that the registration is the best. The black color is also conspicuous, but this is not printed in mixed colors like the other three colors, so the above registration correction is performed.

Next, FIG. 9 shows the registration of print dots when the recording heads 37 of the respective colors are driven in time division as described above. In FIG. 9, the recording head 3 for each color
The pitch (pixel interval) of the print dots by 7 is exactly 63.5 μm in the main scanning direction (pixel interval: 400 in this embodiment).
dpi) is shown. The drive pulse allocation in this case is shown at 95.

As described above, the pixel interval is 63.5.
Since it is μm, the cycle of 91 VE is 6 in actual printing.
This corresponds to 3.5 μm. In this embodiment, the drive pulse width for one recording head is about 1/1 of the VE signal 91.
It is set to 0, and the deviation of registration between adjacent pixels is 6.35 μm as indicated by 92 in FIG. 9, and about 1 is found between the most misaligned pixels (between BK and Y in FIG. 9).
The deviation is 9 μm. The dots 93 are intentionally shifted downward with respect to the dots 94 to make the drawing easier to see, but they are actually printed at the positions aligned with the BK, C, M, and Y of the dots 94.

As described above, in a device for performing color printing by overprinting using a plurality of recording heads, each recording head is driven in a time-sharing manner, so that the current capacity of the head drive power supply is set to one head. Therefore, the cost of the power supply device can be reduced. In addition, the drive pulse is configured to be freely assigned to each color so that registration can be most matched, and deterioration of registration is minimized by time-division driving, providing an inexpensive image forming apparatus with less color misregistration. There is an effect that can be done.

<Embodiment 2> FIG. 10 is a schematic view of an image forming apparatus of the type in which the print width of the recording head is equal to the width of the recording paper.

1001 is a recording sheet, and the recording sheet 1001
Are conveyed in the direction of the arrow. Reference numerals 1002 to 1005 denote recording heads for cyan (C), magenta (M), yellow (Y), and black (BK), respectively. The present embodiment is an example of an apparatus based on such a raster recording system, and each head of C, M, Y, and BK is time-divisionally driven, and the driving order is changed so that the registration deviation of each color is minimized. The registration can be adjusted in the best condition.

<Third Embodiment> FIG. 11 is a diagram showing an example of the timing when the timing of each head drive pulse can be changed within the VE section. By thus shifting the timing within a range where the head drive pulses do not overlap, registration correction can be performed more accurately. And this timing change can be easily realized by a logic circuit.

In the embodiments described above, the ink jet type image forming method has been described, but the application of the present invention is not limited to this. For example, other methods such as a thermal method and an electrostatic method can be applied as long as the apparatus has a plurality of recording heads and sequentially superimposes them to form an image.

The present invention brings excellent effects particularly in an ink jet recording head and a recording apparatus for recording by forming flying droplets by utilizing thermal energy among the ink jet recording systems.

With regard to its typical structure and principle, for example, US Pat. Nos. 4,723,129 and 4740 are applicable.
What is done using the basic principles disclosed in 796 is preferred. This method can be applied to both the so-called on-demand type and continuous type, but especially in the case of the on-demand type, liquid (ink)
By applying at least one drive signal to the electrothermal converter arranged corresponding to the sheet or liquid path in which the liquid crystal is held, which corresponds to the recorded information and causes a rapid temperature rise exceeding nucleate boiling. Since heat energy is generated in the electrothermal converter to cause film boiling on the heat acting surface of the recording head, air bubbles in the liquid (ink) corresponding to this drive signal in a one-to-one correspondence can be formed. It is valid. The liquid (ink) is ejected through the ejection openings by the growth and contraction of the bubbles to form at least one droplet. When the drive signal is pulsed, growth and contraction of the bubbles are immediately and appropriately performed, so that it is possible to achieve ejection of the liquid (ink) with excellent responsiveness, which is more preferable.

As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the rate of temperature rise on the heat acting surface are adopted, excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the straight liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned specifications, A configuration using US Pat. No. 4,558,333 or US Pat. No. 4,459,600, which discloses a configuration in which the heat-acting surface is arranged in a bending region, may be used.

In addition, Japanese Patent Application Laid-Open No. 59-123670 discloses a structure in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters, and a pressure wave of thermal energy is absorbed. It is also possible to adopt a configuration based on Japanese Patent Application Laid-Open No. 59-138461, which discloses a configuration in which the opening corresponds to the ejection portion.

Further, as a full line type recording head having a length corresponding to the width of the maximum recording medium which can be recorded by the recording apparatus, the length can be increased by combining a plurality of recording heads as disclosed in the above-mentioned specification. Either of the structure satisfying the requirement or the structure as one recording head integrally formed may be used.

In addition, by being mounted on the apparatus main body, it can be electrically connected to the apparatus main body and can be supplied with ink from the apparatus main body by a replaceable chip type recording head or the recording head itself. Alternatively, a cartridge type recording head provided with an ink tank may be used.

Further, it is preferable to add a recovery means for the recording head, a preliminary auxiliary means, etc., which are provided as a configuration of the recording apparatus of the present invention, because the effect of the present invention can be further stabilized. .. Specific examples thereof include capping means, cleaning means, pressurizing or suctioning means for the recording head, preheating means using an electrothermal converter or a heating element other than this, or a combination thereof, and recording. It is also effective to perform stable recording by performing a preliminary discharge mode in which another discharge is performed.

Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but the recording head may be integrally formed or a plurality of combinations may be used. Alternatively, the device may be provided with at least one of full colors by color mixing.

In the embodiments of the present invention described above, the ink is described as a liquid, but it is an ink that solidifies at room temperature or lower and softens at room temperature, or is a liquid, or the above-mentioned. In the inkjet method, it is common to adjust the temperature of the ink itself within a range of 30 ° C to 70 ° C to control the temperature of the ink so that the viscosity of the ink is within a stable ejection range. It is sufficient that the ink is liquid.

In addition, the temperature rise due to the thermal energy is positively prevented by using it as the energy for changing the state of the ink from the solid state to the liquid state, or the ink is solidified in a standing state for the purpose of preventing evaporation of the ink. In some cases, whether ink is used, the ink is liquefied by application of thermal energy according to the recording signal and is ejected as a liquid ink, or the one that has already started to solidify when it reaches the recording medium. The use of an ink having a property of being liquefied only by heat energy is also applicable to the present invention. In such a case, the ink is disclosed in JP-A-54-5684.
No. 7 or JP-A No. 60-71260, a mode in which it faces the electrothermal converter in a state of being held as a liquid or solid in the recess or through hole of the porous sheet. May be In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

Further, as a form of the recording apparatus according to the present invention, the recording apparatus according to the present invention is integrally or separately provided as an image output terminal of the information processing equipment such as the word processor and the computer, and is combined with a reader or the like. It may be in the form of a copying machine or a facsimile machine having a transmission / reception function.

Further, the present invention is not limited to the application to a binary image forming apparatus for forming an image by turning dots on and off, and the ink ejection amount is changed for each nozzle and one nozzle is used. Even a multi-valued image forming apparatus capable of producing gradation can be implemented. Also, the number of recording heads is 2
Any device used in the present invention can be used, and the effects of the present invention can be obtained.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device.

[0065]

As described above, according to the present invention, it becomes possible to drive a plurality of recording heads in a time-division manner, thereby reducing the driving power source and providing an inexpensive image forming apparatus. Further, it becomes possible to set which recording head is allocated to the driving timing of each divided recording head, and it is possible to minimize the deviation of registration due to time division driving.

[Brief description of drawings]

FIG. 1 is an external perspective view of a digital color copying machine according to an embodiment.

FIG. 2 is a cross-sectional view of the digital color copying machine of the embodiment.

FIG. 3 is a diagram illustrating a scanning carriage unit according to an embodiment.

FIG. 4 is a diagram illustrating the operation of the recording head.

FIG. 5 is a block diagram of a recording head drive circuit.

FIG. 6 is a detailed block diagram of a timing generation block.

FIG. 7 is a timing chart regarding image data import.

FIG. 8 is a timing chart of head drive pulses.

FIG. 9 is a diagram showing a printing state of one pixel.

FIG. 10 is a diagram illustrating a recording head according to a second exemplary embodiment.

FIG. 11 is a timing chart of drive pulses according to the third embodiment.

[Explanation of symbols]

 1 Image Scanner 2 Controller Section 3 Printer Section 37 Recording Head 51 Timing Generation Blocks 52-55 Recording Head Driving Section 56 Head Drive Power Supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location H04N 1/23 101 C 9186-5C 9211-2C B41J 3/10 101 J

Claims (7)

[Claims] 1. An image forming apparatus having a plurality of recording heads, wherein dots recorded by each of the recording heads are sequentially overlaid to form an image, and each of the recording heads is formed corresponding to recording data. An image forming apparatus comprising: a recording head driving unit that is driven; and a timing generation unit that shifts the driving timing of each recording head by the recording head driving unit so as not to overlap with each other by a predetermined amount. 2. The image forming apparatus according to claim 1, further comprising drive order changing means for changing the order of the drive timings of the recording heads. 3. The image forming apparatus according to claim 1, further comprising a timing changing unit that changes each driving timing of each recording head. 4. The image forming apparatus according to claim 1, wherein each of the recording heads is integrally mounted on a carriage and is driven in synchronization with scanning of the carriage. 5. The image forming apparatus according to claim 1, wherein the recording head is an inkjet recording head that ejects ink to perform recording. 6. The recording head is a recording head that ejects ink by using thermal energy, and is an ink jet recording head that includes a thermal energy converter for generating thermal energy applied to the ink. Item 5
The image forming apparatus described. 7. The recording head causes the ink to cause a state change by the thermal energy applied by the thermal energy converter, and ejects the ink from an ejection port based on the state change. Image forming device.