JP2004351837A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that when recording can be started from the tip of a paper by transferring the paper by a conveyor belt, and a deviation for detecting the tip of the paper is generated, liquid droplets fall down on the conveyor belt to contaminate the conveyor belt. <P>SOLUTION: A paper sensor 41 for detecting the paper 12 transferred by the conveyor belt 21 is provided on a carriage 3 on which a recording head 7 is mounted, and the tip of the paper 12 is detected by the paper sensor 41. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to an image forming apparatus.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-94782
As an image forming apparatus (or also referred to as an image recording apparatus) such as a printer, a facsimile, and a copying apparatus, for example, an ink jet recording apparatus is known. The ink jet recording apparatus includes a sheet (including OHP, etc., which is not limited to paper from an ink recording head. The ink droplet can be attached to a droplet, and is also referred to as a recording medium, a recording medium, a recording paper, or the like. The recording (image formation) is performed by ejecting ink droplets to the high-speed recording of a high-definition image, the running cost is low, the noise is low, and the multicolor ink is used. This makes it easy to record a color image.
[0004]
In such an ink jet recording apparatus, a recording head, which is a means for forming an image, is mounted on a carriage, the carriage is scanned, and a recording medium is conveyed to form an image. Information becomes important. By accurately acquiring the position information of the recording medium, the recording can be started (the start of image formation) from an accurate position, and the quality can be improved.
[0005]
In particular, in an apparatus that conveys a recording medium using a conveyance belt, if ink droplets are ejected from the recording head at a position off the recording medium, the ink droplets land on the conveyance belt and the back surface of the recording medium becomes dirty. Will occur.
[0006]
Here, conventionally, for example, as described in Patent Document 1, a sensor for measuring the paper length is provided, and the sensor detects the paper length (the length in the paper transport direction). is there.
[0007]
Conventionally, the arrival of the recording medium at the image forming unit (recording unit) (detection of the leading end) is performed by a feed amount of the recording medium, a sensor fixed at a certain position, or the like.
[0008]
[Problems to be solved by the invention]
However, if the detection of the leading edge of the recording medium is performed based on the feed amount of the recording medium, it is difficult to control the accurate position due to physical errors such as variations in the set of recording media and deviations generated in the transport mechanism. Also, in the method of detecting a recording medium by attaching the sensor to a fixed position, it is necessary to consider the position of the sensor with respect to the size of the recording medium, which may adversely affect the mechanical layout.
[0009]
There is a similar problem in detecting the width of a recording medium. In other words, when performing a recording operation according to a print command sent from a personal computer or the like, since the recording operation is conventionally performed only according to the print instruction sent from the personal computer, the end of the recording medium may be partially cut, Even when the recording medium is bent, the recording operation has been performed on a place where there is no recording medium. In addition, when the recording medium is conveyed at an angle to the traveling direction, or when the end of the recording medium is partially cut off, there is a similar problem. Preferably it can be done.
[0010]
The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of detecting the leading edge and the sheet width of a sheet with a simple configuration and preventing erroneous recording.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, an image forming apparatus according to the present invention has a configuration in which a carriage is provided with a detecting unit for detecting a leading end of a recording medium.
[0012]
Here, the transmission of the output signal of the detection means can be performed using an analog method, or the transmission of the output signal of the detection means can be performed using a digital method.
[0013]
The image forming apparatus according to the present invention has a configuration in which the carriage is provided with a detecting unit for detecting the width of the recording medium in the scanning direction of the carriage.
[0014]
Here, the transmission of the output signal of the detection means can be performed using an analog method, or the transmission of the output signal of the detection means can be performed using a digital method. Further, it is preferable to perform the operation of detecting the width of the recording medium only at the time of the first scanning of the carriage.
[0015]
In the image forming apparatus according to the present invention, the detecting unit can detect the recording medium on the upstream side in the recording medium transport direction from the image forming start position by the image forming unit, and detect the image forming area at the home position of the carriage. Is preferably located on the side.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a side view for explaining an overall configuration of an ink jet recording apparatus showing an example of an image forming apparatus according to the present invention, FIG. 2 is a plan view showing main parts of the recording apparatus, and FIG. FIG.
[0017]
In this ink jet recording apparatus, a carriage 3 is slidably held in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members which are laterally mounted on left and right side plates (not shown). 2 is moved and scanned in the direction indicated by the arrow in FIG. 2 (main scanning direction).
[0018]
The carriage 3 is provided with a plurality of ink ejection orifices through a recording head 7 composed of four inkjet heads for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk). They are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.
[0019]
As the ink-jet head constituting the recording head 7, a piezoelectric actuator such as a piezoelectric element, a thermal actuator utilizing an electrothermal conversion element such as a heating resistor and utilizing a phase change due to a film boiling of a liquid, and a metal phase change due to a temperature change are used. An actuator having a shape memory alloy actuator to be used, an electrostatic actuator using electrostatic force, or the like as an energy generating means for discharging ink can be used.
[0020]
Further, the carriage 3 is mounted with sub-tanks 8 of each color for supplying each color ink to the recording head 7. The sub tank 8 is supplied with ink from a main tank (ink cartridge) via an ink supply tube (not shown).
[0021]
On the other hand, as a paper feed unit for feeding paper 12 loaded on a paper loading unit (pressure plate) 11 such as a paper feed cassette 10, a half-moon roller that separates and feeds the papers 12 one by one from the paper loading unit 11 ( The paper feed roller 13 and the paper feed roller 13 are provided with a separation pad 14 made of a material having a large coefficient of friction. The separation pad 14 is urged toward the paper feed roller 13.
[0022]
As a transport unit for transporting the paper 12 fed from the paper feed unit below the recording head 7, a transport belt 21 for electrostatically attracting and transporting the paper 12 and a feed belt 21 A counter roller 22 for transporting the paper 12 sent through the guide 15 between the transport belt 21 and the paper 12 transported substantially vertically upward is turned by approximately 90 ° to copy the paper 12 onto the transport belt 21. A transport guide 23 for adjusting the pressure and a pressing roller 25 urged toward the transport belt 21 by a pressing member 24 are provided. Further, a charging roller 26 serving as a charging unit for charging the surface of the transport belt 21 is provided.
[0023]
Here, the transport belt 21 is an endless belt, is stretched between a transport roller 27 and a tension roller 28, and rotates the transport roller 27 from a sub-scanning motor 31 via a timing belt 32 and a timing roller 33. By doing so, it is configured to circulate in the direction indicated by the arrow in FIG. 2 (belt (paper) transport direction).
[0024]
The transport belt 21 has a surface layer serving as a paper adsorption surface formed of a pure resin material having a thickness of about 40 μm, for example, of which resistance is not controlled, for example, an ETFE pure material, and resistance control is performed with carbon using the same material as the surface layer. And a back layer (medium resistance layer, earth layer).
[0025]
A transport roller nip 18 is formed by the transport roller 27 and the counter roller 22, and a paper detection sensor 16 that detects the paper 12 is disposed at a predetermined position upstream of the transport roller nip 18 in the paper transport direction. . The paper detection sensor 16 detects the paper 12 by displacing the detection lever 17 of the paper 12 (the position indicated by the broken line in FIG. 1 is the ON position). The paper detection sensor 16 is for detecting paper feeding.
[0026]
The charging roller 26 is arranged so as to be in contact with the surface layer of the transport belt 21 and rotate following the rotation of the transport belt 21, and apply 2.5 N to both ends of the shaft as a pressing force. The transport roller 27 also functions as an earth roller, and is arranged in contact with the middle resistance layer (back layer) of the transport belt 21 and is grounded.
[0027]
A guide member 36 is arranged on the back side of the transport belt 21 so as to correspond to the printing area of the recording head 4. The guide member 36 has an upper surface protruding toward the recording head 7 from a tangent line of two rollers (the transport roller 27 and the tension roller 28) supporting the transport belt 21. As a result, the transport belt 21 is pushed up and guided by the upper surface of the guide member 36 in the printing area.
[0028]
In order to detect the leading edge of the sheet 12 conveyed by the conveyor belt 21, the carriage 3 is provided with a sheet sensor 41 composed of a reflection type photo sensor as a detecting means, as shown in FIG. The paper sensor 41 is provided on the side located on the recording area (image forming area) side (conveying belt 21 side) when the carriage 3 is at the home position (the position shown by the solid line in FIG. 3).
[0029]
As shown in FIGS. 1 and 3, an encoder scale 42 having a slit is provided on the front side of the carriage 3, and a transmission type photosensor for detecting the slit of the encoder scale 42 is provided on the front side of the carriage 3. And an encoder sensor 43 for detecting the position of the carriage 3 in the main scanning direction (the position with respect to the home position).
[0030]
Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation unit for separating the paper 12 from the transport belt 21, a paper discharge roller 52 and a paper discharge roller 53, and a paper discharge And a discharge tray 54 for storing the sheets 12 to be printed.
[0031]
A double-sided paper feeding unit 61 is detachably mounted on the back. The double-sided paper feeding unit 61 takes in the paper 12 returned by the rotation of the transport belt 21 in the reverse direction, reverses the paper, and feeds the paper 12 again between the counter roller 22 and the transport belt 21.
[0032]
In the ink jet recording apparatus configured as described above, the paper 12 is separated and fed one by one from the paper feeding unit, and the paper 12 fed substantially vertically upward is guided by the guide 15, and the transport belt 21 and the counter roller 22 And the leading end thereof is guided by a carrying guide 23 and pressed against the carrying belt 21 by a leading end pressing roller 25 to change the carrying direction by approximately 90 °.
[0033]
At this time, a positive output and a negative output are alternately repeated from the high voltage power supply to the charging roller 26 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the transport belt 21 alternates, that is, In the sub-scanning direction, which is the circling direction, plus and minus are alternately charged in a belt shape with a predetermined width. When the paper 12 is fed onto the positively and negatively charged conveyor belt 21, the paper 12 is polarized in the paper 12 to a charge opposite to the charged pattern, so that a capacitor connected in parallel is formed. The paper 12 is attracted to the transport belt 21, and the paper 12 is transported in the sub-scanning direction by the orbital movement of the transport belt 21.
[0034]
Then, by driving the recording head 7 in accordance with the image signal while moving the carriage 3, ink droplets are ejected onto the stopped paper 12 to record one line, and after the paper 12 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal indicating that the rear end of the sheet 12 has reached the recording area, the recording operation is terminated, and the sheet 12 is discharged to the discharge tray 44.
[0035]
In the case of double-sided printing, when the recording of the front side (the side to be printed first) is completed, the transported belt 21 is rotated in the reverse direction, so that the recorded paper 12 is fed into the double-sided paper feeding unit 61, The sheet 12 is turned over (with the back side being the printing surface) and fed again between the counter roller 22 and the conveyor belt 21, and the timing is controlled, and the sheet is conveyed onto the conveyor bell 21 in the same manner as described above. After recording on the back surface, the paper is discharged to the paper discharge tray 44.
[0036]
Next, an outline of a control unit of the inkjet recording apparatus will be described with reference to FIG. FIG. 4 is an overall block diagram of the control unit.
The control unit includes a printer controller 70, a motor driver 81 for driving the main scanning motor 4 and the sub-scanning motor 31, and a paper feeding clutch 83 for transmitting the rotation of the sub-scanning motor 31 to the paper feeding roller 13. A driver 82 for driving, a head driver (constituted by a head drive circuit and a driver IC) 84 for driving the recording head 7 (ink jet head), and the like are provided.
[0037]
The printer controller 70 receives, via a cable or a network, an interface (hereinafter referred to as “I”) that receives print data and the like from a host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera. / F ”72), a main control unit 73 including a CPU, etc., a RAM 74 for storing various data, a ROM 75 for storing routines for various data processing, and a drive waveform to the recording head 7. A drive signal generation circuit 77 to be generated, an I / F 78 for transmitting print data and drive waveforms developed into dot pattern data (bitmap data) to the head driver 84, and motor drive data to the motor driver 81. I / F 7 for transmitting clutch-on signal to driver 82 And an equal.
[0038]
The RAM 74 is used as various buffers and a work memory. The ROM 75 stores various control routines executed by the main control unit 73, font data, graphic functions, various procedures, and the like.
[0039]
The main control unit 73 performs paper feed control based on a detection signal from the paper detection sensor 16. The main control unit 73 detects the position of the carriage 3 in the main scanning direction based on the output signal of the encoder 44 to control the stop position of the carriage 3, and based on the detection signal of the paper sensor 42, controls the leading end position of the paper 12. The detection and the presence or absence of the sheet 12 on the transport belt 21 are performed.
[0040]
The main control unit 73 reads and analyzes the print data in the reception buffer included in the I / F 72, stores the analysis result (intermediate code data) in a predetermined area of the RAM 74, and stores the analysis result in the ROM 75 from the stored analysis result. The dot pattern data for outputting an image is generated using the stored font data, and is stored again in a different predetermined area of the RAM 74. When the printer driver on the host side develops the image data into bitmap data and transfers it to this printing apparatus, the received bitmap image data is simply stored in the RAM 74.
[0041]
When the dot pattern data corresponding to one row of the recording head 7 is obtained, the main control unit 73 synchronizes the dot pattern data for one row with the clock signal CLK from the oscillation circuit 76, and The data is transmitted as serial data to the head driver 82 via / F78, and a latch signal is transmitted to the head driver 82 at a predetermined timing.
[0042]
The drive signal generation circuit 77 stores a drive waveform (drive signal) pattern data in a ROM (which can also be constituted by a ROM 75), and a D / A that performs D / A conversion on the drive waveform data read from the ROM. It is composed of a waveform generation circuit including a converter, an amplifier, and the like.
[0043]
The head driver 82 includes a shift register that inputs a clock signal from the main control unit 73 and serial data that is a print signal, a latch circuit that latches a register value of the shift register with a latch signal from the main control unit 73, and a latch circuit. A level conversion circuit (level shifter) for changing the level of the output value and an analog switch array (switch means) whose on / off is controlled by the level shifter. The drive waveform is obtained by controlling on / off of the analog switch array. Are selectively applied to the head 7.
[0044]
Next, an outline of print control (recording control) by the main control unit 73 will be described with reference to FIGS.
Prior to sheet feeding, the main control unit 73 drives the main scanning motor 4 to rotate the main scanning motor 4 to move the carriage 3 at the non-recording position as shown in FIG. Then, after being positioned at a substantially central portion of the transport belt 21 (or a substantially central portion of a sheet of a sheet size to be fed), the sheet feeding clutch 83 is turned on to apply the rotation of the sub-scanning motor 31 to the sheet feeding roller 13. As a result, the paper feed roller 13 makes one rotation clockwise, and the paper 12 is separated from the paper feed tray 10 by the friction pad 14 and sent out.
[0045]
Then, the detection signal of the paper sensor 41 is checked to determine whether or not the leading edge of the paper 12 has been detected, and the paper 12 is conveyed (fed) to a predetermined printing start position from the time when the leading edge of the paper 12 is detected. Stop. In this case, as shown in FIG. 8, if the paper sensor 41 is provided at a position where the leading end of the paper 12 is detected upstream of the printing area (image forming area) by the recording head 7 in the paper transport direction, Even if the detection position shift of the leading end of the paper 12 occurs, the paper 12 can be reliably sent to the printing start position. Absent.
[0046]
Thereafter, the carriage 3 is temporarily returned to the home position, and movement of the carriage 3 to the recording area side is started based on the output of the encoder 44 with reference to the home position. It is determined whether or not the sheet 12 is present. When the sheet 12 is present, a required printing (recording operation) is performed, and when the sheet 12 is not detected, the recording operation is not performed. Accordingly, printing (ink droplet ejection) is not performed in a portion where the paper 12 is not present, so that ink droplets are not ejected onto the transport belt 21 and contamination of the transport belt 21 and the paper 12 can be prevented.
[0047]
Next, processing when a reflection type photosensor is used as the paper sensor 41 will be described.
The reflection type photo sensor is an element that converts the amount of light reflection into a voltage and outputs the voltage. When a reflection type photo sensor is used, the sensor is mounted in the direction facing the paper, and the light between the transport belt 21 and the paper 12 is The presence or absence of the paper 12 is detected using the difference in the amount of reflection caused by the difference in the reflectance.
[0048]
FIG. 9 shows an example of a circuit configuration in the case where this reflection type photosensor is used. In this circuit configuration, the reflection type photo sensor 41A having the light emitting element 41Aa and the light receiving element 41Ab detects the paper 12 on the transport belt 21 and converts an electric signal (output signal) output from the reflection type photo sensor 41 into a voltage. The data is input to a recording control IC 103 that controls a recording operation and the like configuring the control unit 70 via a follower circuit 101.
[0049]
That is, since the electric signal output from the sensor 41A is very weak, the voltage follower circuit 101 is configured by an operational amplifier having a high input impedance, and the output level of the sensor is stabilized. In addition, since the physical positional relationship between the sensor position and the recording control IC 103 is often distant, the voltage follower circuit is effective as a measure against noise. In this case, the input of the recording control IC 103 is made to correspond to an analog signal, and an A / D converter is mounted inside to perform A / D conversion for processing.
[0050]
In this case, the advantage of transmitting the output signal of the sensor as an analog signal will be briefly described. FIG. 10 shows an output signal from the reflection type photo sensor. As shown in the drawing, it takes a certain time from the time t1 when the paper 12 actually reaches the sensor 41A to the time t2 when the threshold voltage Vref is regarded as paper detection in the recording control IC 103. Therefore, the accuracy of position detection changes depending on how many volts the threshold voltage Vref is set.
[0051]
Further, since the reflection coefficient differs depending on the type of paper, the amplitude of the voltage of the signal output from the photosensor 41A also changes as shown in FIG. Therefore, by transmitting and processing the output signal of the sensor in an analog manner, the detection accuracy can be improved by setting the threshold voltage to be lower, and the optimum threshold can be set for each paper. Become like
[0052]
Next, another example of a circuit configuration in the case of using a reflection type photosensor is shown in FIG. In this circuit configuration, the reflection type photo sensor 41A detects the paper 12 on the transport belt 21 and controls an electric signal (output signal) output from the reflection type photo sensor 41 via the Schmitt trigger input buffer element 104. The data is input to a recording control IC 103 that controls the recording operation and the like constituting the unit 70.
[0053]
That is, this circuit configuration transmits and processes the output signal of the photosensor in a digital manner. Although the output of the sensor 41A may be directly input to the recording control IC 103, the buffer element 104 is arranged at a position close to the sensor 41A for the purpose of stabilizing the output level of the sensor and taking measures against noise. As the buffer element 104, a C-MOS type having a high input impedance is used, and a Schmitt trigger input type having a hysteresis characteristic is used because the input is an analog signal.
[0054]
By transmitting and processing in a digital manner in this manner, the circuit can be configured at low cost, and is transmitted with information of "0" and "1", so that it is less affected by noise. To this end, as described above, it is preferable that the buffer element be disposed near the sensor, for example, on the carriage 3.
[0055]
Next, detection of the sheet width (length in the carriage scanning direction) will be described with reference to FIG.
Here, as described above, after detecting the leading end of the paper 12, the paper 12 is transported to a position where the sensor 41 can scan the paper 12, and the carriage 3 is moved along the x-axis as shown in FIG. In the direction (main scanning direction), the sensor 41 detects the area where the sheet 12 exists. At this time, since the output from the sensor 41 changes like the output signal transition characteristic shown in FIG. 3B, the width of the sheet 12 can be detected by processing this output signal.
[0056]
In this case, the circuit configuration when a reflective photosensor is used as the sensor 41 is the same as that in FIG. 9 or FIG. Further, the detection of the width of the sheet is performed only for the first scan after the sheet is conveyed, so that the processing can be reduced.
[0057]
In the above embodiment, the present invention is applied to a shuttle type ink jet recording apparatus using a carriage. And the like.
[0058]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, since the carriage is provided with the means for detecting the leading end or the width of the recording medium, the leading end and the sheet width can be detected with a simple configuration. As a result, erroneous recording can be prevented.
[Brief description of the drawings]
FIG. 1 is a side view illustrating an example of an image forming apparatus according to the present invention. FIG. 2 is a plan view illustrating a main part of the apparatus. FIG. 3 is a perspective view illustrating a main part of the apparatus. FIG. FIG. 5 is a block diagram for explaining the outline of the unit. FIG. 5 is a flowchart for explaining an example of control by the control unit. FIG. 6 is a schematic plan explanatory diagram for explaining the control. FIG. FIG. 8 is a schematic plan view for explaining another example of the mounting position of the paper sensor. FIG. 9 is a block diagram for explaining an example of a circuit configuration for transmitting an output signal from the paper sensor. FIG. 10 is an explanatory diagram for explaining a change in the output signal of the paper sensor. FIG. 11 is an explanatory diagram for explaining a change in the output signal of the paper sensor due to the reflectance of the paper. FIG. 12 is a circuit for transmitting an output signal from the paper sensor. Block explanatory diagram for explaining another example of the configuration 3 is an explanatory diagram for explaining the paper width detection DESCRIPTION OF SYMBOLS
3 carriage, 7 recording head, 10 paper feed tray, 12 paper, 13 paper feed roller, 15 guide, 16 paper detection sensor, 21 transport belt, 22 counter roller, 26 charging roller, 27: transport roller, 28: tension roller, 41: paper sensor (detection means).

Claims (8)

In an image forming apparatus for forming an image on a recording medium by scanning a carriage equipped with a unit for performing recording, the carriage includes a detecting unit for detecting a leading end of the recording medium. Image forming device. 2. The image forming apparatus according to claim 1, wherein the output signal of the detection unit is processed by using an analog method. 2. The image forming apparatus according to claim 1, wherein the output signal of the detection unit is processed using a digital method. An image forming apparatus for forming an image on a recording medium by scanning a carriage equipped with a unit for performing recording is provided with a detecting unit for detecting a width of the recording medium in the scanning direction of the carriage. An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein the output signal of the detection unit is processed by using an analog method. 6. The image forming apparatus according to claim 5, wherein the output signal of the detection unit is processed using a digital method. 7. The image forming apparatus according to claim 4, wherein an operation of detecting a width of the recording medium is performed only at a first scanning of the carriage. The image forming apparatus according to claim 1, wherein the detection unit is capable of detecting the recording medium at a position upstream of an image formation start position by the unit that forms the image in a recording medium conveyance direction, and An image forming apparatus, which is located on an image forming area side at a home position of a carriage.

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