JPH08142346A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To form an image free from density irregularity by making the temps. of the respective dot forming means of a recording head same at the time of the formation of dots. CONSTITUTION: Image data VID is converted to parallel data by a shift register 702 to be latched by a latch 705. When a DSEL signal is 'H', a nozzle heater 707 is driven on the basis of the latched parallel data through a selector 705 and a drive transistor 706. When the succeeding DSEL signal is 'L', the selector 705 is changed over and the parallel data due to normal image data is reversed by an inverter 708 and the nozzle heater 707 is driven on the basis of the data obtained by reversal. At this time, pulse width is narrowed so as to become energy level not reaching the emission of ink. By this constitution, all of nozzles are driven in synchronous relation to dot forming timing without relying on image data and the temps. of the respective nozzles at the time of the driving of the nozzles become same and density irregularity is eliminated.

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 such as a printer or a copying machine, and more particularly to driving a thermal ink jet multi recording head (hereinafter referred to as multi head) having a plurality of nozzles arranged in-line (series). is there.

[0002]

2. Description of the Related Art When an image is formed by a multi-head, the ejection frequency of each nozzle varies depending on the image to be recorded, and as a result, the temperature of each nozzle differs. The temperature difference between the nozzles appears as uneven density in the recorded image. In recent years, various proposals have been made to prevent the occurrence of density unevenness due to higher image quality and colorization of copying machines and printers.

In addition to dot formation, a heater and a cooling element are provided in the multi-head to control the temperature so that the multi-head has a constant temperature, or the heating element of the multi-head is driven within a range that does not result in ejection. Those that do are proposed.

[0004]

However, in the above-mentioned conventional example, regardless of the ejection timing or the image data,
Even if processing is performed uniformly for all nozzles, or even if the heating elements are driven in a range that does not result in ejection in accordance with image data, they are driven asynchronously with the dot formation timing, so The nozzle temperatures cannot be equal.

The present invention has been made in view of the above problems of the conventional example, and the temperature of each dot forming means of the recording head becomes the same at the time of dot formation, and an image can be formed without density unevenness. An object is to provide a forming apparatus.

[0006]

In order to achieve the above-mentioned object, in the present invention, an image forming apparatus has the following (1), (2),
Configure as in (3).

(1) An image forming apparatus for forming an image by a recording head in which a plurality of dot forming means driven by electro-thermal converting elements are arranged, wherein the image forming of the plurality of dot forming means is performed. An image forming apparatus provided with a biasing unit that biases an electro-thermal conversion element of a dot forming unit that does not perform dot formation at a level that does not lead to dot formation, in synchronization with dot formation timing.

(2) The image forming apparatus according to (1), wherein the dot forming means is of an ink jet type.

(3) The urging means urges the dot forming means arranged at the end of the recording head at a higher level than the dot forming means arranged at the central part. The image forming apparatus according to (2) above.

[0010]

With the configurations (1), (2), and (3), the dot forming means that does not form dots during image formation is synchronized with the dot formation timing and is energized at a level that does not lead to dot formation. To be done.

In the configuration (3), the dot forming means arranged at the end of the recording head is urged by the urging means at a higher level than the dot forming means arranged in the central portion.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples.

(Embodiment 1) FIG. 1 is an external perspective view of a "digital full color copying machine" which is Embodiment 1. In the upper part of the figure, a color image scanner unit 1 (hereinafter referred to as a scanner unit) that reads a document image and outputs digital full-color image data, and various image processing of digital color image data built in the scanner unit 1 are performed. The controller unit 2 has a processing function such as an interface with an external device.

The lower part of FIG. 1 shows a printer section 3 for recording a color digital image signal output from the controller section 2 on a recording sheet.

The above-mentioned two parts can be separated from each other, and can be installed at remote places by extending the connecting cable.

FIG. 2 is a side sectional view showing the internal structure of the digital color copying machine of FIG.

First, the exposure lamp 14, the lens 15, the CCD image sensor 16 capable of reading a line image in full color, the original image placed on the original platen glass 17, the projected image by the projector, or the feeding mechanism 12. Read the sheet document image. Next, various image processing is performed by the scanner unit 1 and the controller unit 2,
The printer unit 3 records on recording paper.

In FIG. 2, the recording paper is a small-sized standard size (A4 to A3 size in this embodiment) sheet feed cassette 20 for storing cut paper and a large size (A2 to A1 size in this embodiment) recording. The paper is fed from the roll paper 29 for performing. Further, as for paper feeding, by inserting the recording paper one by one from the manual feeding port 22 of FIG. 1 along the paper feeding unit cover 21, it is possible to feed paper from the outside of the apparatus (manual feeding).

The pickup roller 24 is a roller for feeding cut sheets one by one from the sheet feeding cassette 20, and the fed cut sheets are conveyed to the first feeding roller 26 by the cut sheet feeding roller 25. It The roll paper 29 is sent out by the roll paper feed roller 30, cut into a standard length by the cutter 31, and conveyed to the paper feed first roller 26. Similarly, the manual feed roller 32 conveys the paper to the first paper feed roller 26.

Pickup roller 24, cut paper feed roller 25, roll paper feed roller 30, paper feed first roller 2
6, the manual feed roller 32 is a paper feed motor (not shown) (for example,
It is driven by a DC servo motor), and on / off control can be performed at any time by an electromagnetic clutch attached to each roller.

When the printing operation is instructed by the controller unit 2, the recording paper which is selectively fed due to the deviation of the paper feeding path is conveyed to the first feeding roller 26. After forming a predetermined amount of paper loop to remove the skew of the recording paper, the first paper feed roller 26 is turned on to convey the recording paper to the second paper feed roller 27.

First paper feed roller 26 and second paper feed 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. The buffer amount detection sensor 33 is a sensor for detecting the buffer amount. By constantly making the buffer during the paper conveyance, it is possible to reduce the load applied to the paper feed roller 28 and the second paper feed second roller 27, especially when a large-sized recording paper is conveyed, and an accurate paper feed operation is possible. become.

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. At this time, while the drive system is detected by the buffer amount detection sensor 33 by the sheet feeding motor, control is performed so that the buffer amount is always a predetermined value. The printed recording paper is ejected to the paper ejection tray 23 to complete the printing operation.

FIG. 3 shows the scanning carriage 3 in the first embodiment.
It is a figure which shows the structure of 4 circumference | 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 second sheet feeding roller 27 is driven via the second sheet feeding roller clutch 43. The scanning motor 35 is the scanning carriage 3
4 is a drive source for scanning 4 in the directions of arrows A and B via the scanning belt 34. Since accurate paper feed control is required in this embodiment, the paper feed motor 40 and the scanning motor 3
5 uses a pulse motor. When the recording paper reaches the second paper feed roller 27, the second paper feed roller clutch 43,
The paper feed motor 40 is turned on to move the recording paper to the paper feed roller 28.
Is conveyed to the platen 39. Platen 39 for recording paper
The sensor information detected by the paper detection sensor 44 provided above is used for position control and jam control.

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 moved to the position of the home position sensor 41, and then the forward scanning is performed in the direction of arrow A, and cyan C, magenta M, Yellow Y, Black K
The ink is ejected from the recording head 37 to record an image.
When the image recording for a predetermined length is completed, the scanning carriage 34
Then, the scanning carriage 34 is returned to the position of the home position sensor 41 through the backward scan in the direction of arrow B. During the backward scan, the paper feed by the length recorded by the print head 37 is performed in the direction of arrow C by driving the paper feed roller 28 by the paper feed motor 40.

In the present embodiment, the recording head 37 is an ink jet nozzle of the above-mentioned system, and four nozzles each having 256 nozzles assembled in Y, M, C and K are used.

When the scanning carriage 34 is stopped at the home position detected by the photo sensor 41, 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, etc. Paper time,
This is a process of performing a pressurizing operation to the recording head 37, an idle ejection operation of ink, and the like under pre-programmed conditions such as the temperature inside the apparatus and the ejection time.

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

Next, the operation of the scanner section 1 will be described.

FIG. 4 is a diagram showing the internal mechanism of the scanner unit 1 in the first embodiment. CCD unit 18 is a CCD
A main scanning motor 50 and a pulley 5 fixed on a rail 54, which is a unit composed of 16, a lens 15 and the like.
A drive system in the main scanning direction composed of 1, a pulley 52 and a wire 53 is used to move and read. The light shielding plate 55 and the home position sensor 56 are used for position control when the CCD unit 18 is moved to the home position for main scanning in the correction area 68 in the figure.

The rail 54 is mounted on the rails 65 and 69, and has a sub-scanning motor 60 and pulleys 67, 68, 71 and 7.
It is moved by a drive system in the sub-scanning direction composed of 6, shafts 72, 73 and wires 66, 70. The light shielding plate 57 and the home position sensors 58 and 59 are used for position control when moving the rail 54 to the respective sub-scanning home positions in the book mode for reading a document such as a book placed on the document glass 17. .

The sheet feeding motor 61, the sheet feeding rollers 74 and 75, the pulleys 62 and 64, and the wire 63 are mechanisms for feeding the sheet original. This mechanism is a mechanism for feeding a sheet original placed downward on the original glass 17 by the sheet feeding rollers 74 and 75 by a predetermined amount.
FIG. 5 is a diagram for explaining the reading operation in the book mode and the sheet mode according to this embodiment. In book mode,
The CCD unit 18 is moved to the illustrated book mode home position (indicated by the book mode HP in the drawing) in the correction area indicated by 68 in FIG. 5, and the entire surface of the original placed on the original glass 17 is read from there. Start operation.

In the correction area 68, prior to scanning the original,
Set the parameters required for processing such as shading correction, black level correction, and color correction. Then, the main scanning motor 50 starts scanning in the main scanning direction in the direction of the arrow shown. When the reading operation of the area shown by is completed, the main scanning motor 50 is rotated in the reverse direction and the sub scanning motor 6
0 is driven, and the correction area 68 of the area is moved in the sub-scanning direction. Then, similar to the main scanning of the area
If necessary, shading correction, black level correction, color correction, and other processing are performed, and the area reading operation is performed.

By repeating the above scanning, the reading operation of the entire area of (1) is performed, and after the reading operation of the area of (3) is completed, the CCD unit 18 is returned to the book mode home position again.

In the present embodiment, since the document table glass 17 can read a document of maximum A2 size, it is necessary to actually scan a larger number of times, but in the present description, it is simplified for easy understanding of the operation. There is.

In the seat mode, the CCD unit 18
Is moved to the illustrated sheet mode home position (sheet mode HP), and the area of is repeatedly read by reading the sheet original while intermittently operating the sheet feeding motor 61 to read the entire surface of the original sheet.

In the correction area 68 before scanning the original,
Processing such as shading correction, black level correction, and color correction is performed, and then the main scanning motor 50 is moved in the direction of the arrow shown in the figure.
Thus, scanning in the main scanning direction is started. When the reading operation of the forward path of the area is completed, the main scanning motor 50 is rotated in the reverse direction, and the sheet feeding motor 61 is driven during the scanning of the backward path to move the sheet original by a predetermined amount in the sub scanning direction. Subsequently, the same operation is repeated to read the entire surface of the sheet original.

Assuming that the above-described reading operation is the same-magnification reading operation, the area that can be read by the CCD unit 18 is actually a wide area as indicated by the arrow on the left side of FIG. This is because the digital color copying machine of this embodiment has a variable magnification function for enlargement and reduction. That is, as described above, the recording area of the recording head 37 is 1
Since it is fixed at 256 bits per time, for example, 50%
This is because the image information of the 512-bit area which is at least doubled is required to perform the reduction operation of. Therefore, the scanner unit 1 has a built-in function of reading and outputting image information of an arbitrary image area by one main scanning reading.

FIG. 6 is a block diagram showing the arrangement of the digital color copying machine of the first embodiment. In the figure, the control unit 1
Reference numerals 02, 111, and 121 are control circuits for controlling the scanner unit 1, the controller unit 2, and the printer unit 3, respectively, and are configured by a microcomputer, a program ROM, a data memory, a communication circuit, and the like. Control unit 102,
A communication line connects between 111 and the control units 111 and 121, and the control unit 10 is instructed by the control unit 111.
The so-called master-slave control format in which the 2 and 121 operate is adopted.

When operating as a color copying machine, the control unit 111 operates according to input instructions from the control unit 10 and the digitizer 114.

Reference numeral 116 in FIG. 6 is a block for controlling the ejection of the heads 117 to 120, and performs ejection control to which the present invention is applied. 7 is block 11 of FIG.
6 is a block diagram describing in detail one head in FIG. 6, and FIG. 8 is a diagram illustrating the timing thereof. (The other heads have the same circuit, so the description thereof will be omitted.) Detailed description will be given with reference to FIGS. 7 and 8. A portion 708 surrounded by a broken line in FIG.
7 to 120, which are the parts respectively mounted, and the preceding stage is the discharge control unit 116 in FIG.

In FIG. 7, reference numeral 702 denotes a 256-bit shift register, which stores the image data (VID) serially sent in synchronization with the image clock (VCLK).
It is converted into parallel data of 256 dots which is the number of nozzles of the recording head. The parallel-converted image data is latched by the latch circuit 703 and then drives the nozzle heater (electro-thermal conversion element) 707 of each nozzle via the selector 705 and the drive transistor 706 (this causes ink to be ejected to form a recording dot). Form). The recording head is composed of 4 blocks with 64 nozzles as one block. Driving is performed while shifting the timing for each block. This is Vop when driving the nozzle
This is because the peak value of the electric current is suppressed to a small value, and although the ejection timing is off, this deviation is so small that it cannot be determined in the formed image. Next, the drive timing of the recording head will be described with reference to FIG. The HSYNC signal 802 is a signal output for every 256 pieces of image data synchronized with the image clock 801, and is used as a latch clock of the latch 703. This causes the latch 703
In this case, the image data parallel-converted by the shift register 702 is held for one cycle of the HSYNC signal 802. This image data is output by the signals 804 to 812 generated by the timing control unit 701.
It is supplied to each nozzle of the recording head. Of course, the HSYNC signal 802 is set to be equal to the maximum ejection frequency of the recording head so that the recording speed becomes the highest.

Latch 703 by HSYNC signal 802
The image data latched in the DRV0 to DRV3 8
The drive transistor Tr 706 is driven by the pulse signals of 04 to 807, the nozzle heater 707 is heated in a pulse shape, and this causes a state change in the ink, thereby ejecting an ink droplet from the ejection port. Then DR
The nozzle heater 707 is driven by the pulse signals V0 to DRV3 808 to 811. At this time, the pulse width is narrowed so as to supply energy that does not reach ink ejection. Furthermore, when this non-ejection pulse is applied, DSE
When the selector 705 is switched by the L signal 812 and the image data obtained by inverting the normal image data by the inverter 708 is supplied, when the ejection pulses 804 to 807 are applied,
Energy is supplied only to the nozzles in which the image data is "0" and ink is not ejected. As a result, all nozzles are driven in synchronism with the dot formation timing regardless of the image data, and the thermal energy supplied to each nozzle is almost the same. Therefore, it is possible to prevent the occurrence of density difference due to the temperature difference of each nozzle. Therefore, it is possible to obtain a high-quality recorded image without density unevenness.

Although not shown in this embodiment, a heater for heating and cooling the entire recording head, a cooling fan, and a temperature detection sensor are provided, and they are kept at a constant temperature by the control unit 121 in FIG. Like the temperature control. As a result, the temperature of the entire recording head is adjusted, and the temperature variation among the nozzles is corrected by controlling the drive pulse of each nozzle.

(Embodiment 2) Embodiment 1 is an example in which the present invention is applied to a block drive type recording head.
In contrast to the embodiment in which ejection / non-ejection pulses are alternately applied to the recording head, this embodiment describes an example of a recording head in which each nozzle can be driven independently. In the case of such a recording head, the driving according to the first embodiment can be performed, but the driving method described in the present embodiment can be used to more easily perform the driving.

9 and 10 are views for explaining this embodiment. In the timing control unit 901, 100 in FIG.
2,1001 DRV0 and DRV1 signals are HSYN
It is generated in synchronization with the C signal 802. The DRV0 signal is an ejection pulse, and the DRV1 signal is a non-ejection pulse. The DRV0 signal is ANDed with the individual image data (VID), and ink is ejected only when the image data is "1". When the image data is "0", the ejection pulse by DRV0 is not output, but the DR connected to the OR circuit in the next stage
A non-ejection pulse is applied by the V1 signal. As described above, in this embodiment, all nozzles can be driven with a simpler configuration, and the same effect as that of the first embodiment can be obtained.

(Embodiment 3) Even in the system to which Embodiments 1 and 2 are applied, when the temperature gradient of the recording head is strictly observed, the temperature of the nozzle located at the end is lower than that of the other nozzles. There is. This is because the non-ejection pulse applied to each nozzle is constant, and thus the nozzles at the end portions have less thermal energy accumulation. To correct this, the width of the non-ejection pulse can be widened for the end nozzles, and the pulse width can be narrowed for the central portion to reduce the temperature gradient of each nozzle,
A higher effect of preventing uneven density can be obtained.

(Others) The present invention can be widely applied to general thermal recording heads such as thermal recording heads in addition to thermal ink jet recording heads, and is effective in performing high-quality recording with little density unevenness.

[0051]

As described above, in the present invention, the dot forming timing is synchronized with the recording head, and the dot forming means that does not perform dot formation is energized at a level that does not result in dot formation. By doing so, it becomes possible to keep the temperature of all the dot forming means substantially the same,
It is possible to prevent the occurrence of density unevenness due to the temperature difference of each dot forming means, and it is effective in improving the image quality of a recorded image.

[Brief description of drawings]

FIG. 1 is an external perspective view of a first embodiment.

FIG. 2 is a side sectional view of the first embodiment.

FIG. 3 is a diagram showing a configuration around a carriage in the first embodiment.

FIG. 4 is a diagram showing a mechanism inside the scanner according to the first embodiment.

FIG. 5 is an explanatory diagram of a reading operation in a book mode and a sheet mode according to the first embodiment.

FIG. 6 is a diagram showing the configuration of the first embodiment.

7 is a detailed view of block 116 of FIG.

8 is a timing chart of the circuit of FIG.

FIG. 9 is a block diagram of a main part of the second embodiment.

FIG. 10 is a timing chart of essential parts of the second embodiment.

[Explanation of symbols]

 703 Latch circuit 705 Selector 707 Nozzle heater 708 Inverter

Claims (3)

[Claims] 1. An image forming apparatus for forming an image by a recording head in which a plurality of dot-forming means driven by electro-thermal conversion elements are arranged, wherein the plurality of dot-forming means forms an image. An image forming apparatus comprising: an urging unit that urges an electro-thermal conversion element of a dot forming unit that does not form a dot at a level that does not lead to dot formation, in synchronization with dot formation timing. 2. The image forming apparatus according to claim 1, wherein the dot forming means is of an inkjet type. 3. The urging means urges the dot forming means arranged at the end of the recording head at a higher level than the dot forming means arranged at the center. The image forming apparatus according to claim 1 or 2.